Minimum number of intervals to cover the target interval
Last Updated :
23 Jul, 2025
Given an array A[] consisting of N intervals and a target interval X, the task is to find the minimum number of intervals from the given array A[] such that they entirely cover the target interval. If there doesn't exist any such interval then print "-1".
Examples:
Input: A[] = {{1, 3}, {2, 4}, {2, 10}, {2, 3}, {1, 1}}, X = {1, 10}
Output: 2
Explanation:From the given 5 intervals, {1, 3} and {2, 10} can be selected. Therefore, the points in the range [1, 3] are covered by the interval {1, 3} and the points in the range [4, 10] are covered by the interval {2, 10}.
Input: A[] = {{2, 6}, {7, 9}, {3, 5}, {6, 10}}, X = {1, 4}
Output: -1
Explanation: There exist no set of intervals in the given array A such that they cover the entire target interval.
Approach: The given problem can be solved by using a Greedy Approach. It can be observed that the most optimal choice of the interval from a point p in the target range is the interval (u, v) such that u <= p and v is the maximum possible. Using this observation, follow the steps below to solve the given problem:
- Sort the given array A[] in increasing order of the starting points of the intervals.
- Create a variable start and initialize it with the starting point of the target interval X. It stores the starting point of the currently selected interval. Similarly, the variable end stores the ending point of the current variable. Initialize it with start - 1.
- Create a variable cnt, which stores the count of the number of selected intervals.
- Iterate through the given array A[] using a variable i.
- If the starting point of the ith interval <= start, update the value of end with the max(end, ending point of the ith interval), else set start = end and increment the value of cnt by 1.
- If the starting point of the ith interval > end or the value of end is already greater than the ending point of the target interval, break the loop.
- Return -1 if the value of end < ending point of target interval, else return the value of cnt.
Below is the implementation of the above approach:
C++
// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;
// Function to find the minimum number
// of intervals in the array A[] to
// cover the entire target interval
int minimizeSegment(vector<pair<int, int> > A,
pair<int, int> X)
{
// Sort the array A[] in increasing
// order of starting point
sort(A.begin(), A.end());
// Insert a pair of INT_MAX to
// prevent going out of bounds
A.push_back({ INT_MAX, INT_MAX });
// Stores start of current interval
int start = X.first;
// Stores end of current interval
int end = X.first - 1;
// Stores the count of intervals
int cnt = 0;
// Iterate over all the intervals
for (int i = 0; i < A.size();) {
// If starting point of current
// index <= start
if (A[i].first <= start) {
end = max(A[i++].second, end);
}
else {
// Update the value of start
start = end;
// Increment the value
// of count
++cnt;
// If the target interval is
// already covered or it is
// not possible to move
// then break the loop
if (A[i].first > end
|| end >= X.second) {
break;
}
}
}
// If the entire target interval
// is not covered
if (end < X.second) {
return -1;
}
// Return Answer
return cnt;
}
// Driver Code
int main()
{
vector<pair<int, int> > A = {
{ 1, 3 }, { 2, 4 }, { 2, 10 }, { 2, 3 }, { 1, 1 }
};
pair<int, int> X = { 1, 10 };
cout << minimizeSegment(A, X);
return 0;
}
// Java program for the above approach
import java.util.ArrayList;
import java.util.Comparator;
class GFG
{
static class Pair
{
int first;
int second;
public Pair(int f, int s)
{
this.first = f;
this.second = s;
}
}
// Function to find the minimum number
// of intervals in the array A[] to
// cover the entire target interval
public static int minimizeSegment(ArrayList<Pair> A, Pair X)
{
// Sort the array A[] in increasing
// order of starting point
final Comparator<Pair> arrayComparator = new Comparator<GFG.Pair>() {
@Override
public int compare(Pair o1, Pair o2) {
return Integer.compare(o1.first, o2.first);
}
};
A.sort(arrayComparator);
// Insert a pair of INT_MAX to
// prevent going out of bounds
A.add(new Pair(Integer.MAX_VALUE, Integer.MIN_VALUE));
// Stores start of current interval
int start = X.first;
// Stores end of current interval
int end = X.first - 1;
// Stores the count of intervals
int cnt = 0;
// Iterate over all the intervals
for (int i = 0; i < A.size();) {
// If starting point of current
// index <= start
if (A.get(i).first <= start) {
end = Math.max(A.get(i++).second, end);
} else {
// Update the value of start
start = end;
// Increment the value
// of count
++cnt;
// If the target interval is
// already covered or it is
// not possible to move
// then break the loop
if (A.get(i).first > end
|| end >= X.second) {
break;
}
}
}
// If the entire target interval
// is not covered
if (end < X.second) {
return -1;
}
// Return Answer
return cnt;
}
// Driver Code
public static void main(String args[]) {
ArrayList<Pair> A = new ArrayList<Pair>();
A.add(new Pair(1, 3));
A.add(new Pair(2, 4));
A.add(new Pair(2, 10));
A.add(new Pair(2, 3));
A.add(new Pair(1, 1));
Pair X = new Pair(1, 10);
System.out.println(minimizeSegment(A, X));
}
}
// This code is contributed by saurabh_jaiswal.
# Function to find the minimum number
# of intervals in the array A[] to
# cover the entire target interval
def minimizeSegment(A, X):
# Sort the array A[] in increasing
# order of starting point
A.sort()
# Insert a pair of (float('inf'), float('inf'))
# to prevent going out of bounds
A.append((float('inf'), float('inf')))
# Stores start of current interval
start = X[0]
# Stores end of current interval
end = X[0] - 1
# Stores the count of intervals
cnt = 0
# Iterate over all the intervals
i = 0
while i < len(A):
# If starting point of current
# index <= start
if A[i][0] <= start:
end = max(A[i][1], end)
i += 1
else:
# Update the value of start
start = end
# Increment the value
# of count
cnt += 1
# If the target interval is
# already covered or it is
# not possible to move
# then break the loop
if A[i][0] > end or end >= X[1]:
break
# If the entire target interval
# is not covered
if end < X[1]:
return -1
# Return Answer
return cnt
# Driver Code
A = [
(1, 3), (2, 4), (2, 10), (2, 3), (1, 1)
]
X = (1, 10)
print(minimizeSegment(A, X))
// C# program for the above approach
using System;
using System.Collections.Generic;
public class GFG
{
public class Pair
{
public int first;
public int second;
public Pair(int f, int s) {
this.first = f;
this.second = s;
}
}
// Function to find the minimum number
// of intervals in the array []A to
// cover the entire target interval
public static int minimizeSegment(List<Pair> A, Pair X) {
// Sort the array []A in increasing
// order of starting point
A.Sort((a,b)=>a.first-b.first);
// Insert a pair of INT_MAX to
// prevent going out of bounds
A.Add(new Pair(int.MaxValue, int.MinValue));
// Stores start of current interval
int start = X.first;
// Stores end of current interval
int end = X.first - 1;
// Stores the count of intervals
int cnt = 0;
// Iterate over all the intervals
for (int i = 0; i < A.Count;) {
// If starting point of current
// index <= start
if (A[i].first <= start) {
end = Math.Max(A[i++].second, end);
} else {
// Update the value of start
start = end;
// Increment the value
// of count
++cnt;
// If the target interval is
// already covered or it is
// not possible to move
// then break the loop
if (A[i].first > end || end >= X.second) {
break;
}
}
}
// If the entire target interval
// is not covered
if (end < X.second) {
return -1;
}
// Return Answer
return cnt;
}
// Driver Code
public static void Main(String []args) {
List<Pair> A = new List<Pair>();
A.Add(new Pair(1, 3));
A.Add(new Pair(2, 4));
A.Add(new Pair(2, 10));
A.Add(new Pair(2, 3));
A.Add(new Pair(1, 1));
Pair X = new Pair(1, 10);
Console.WriteLine(minimizeSegment(A, X));
}
}
// This code is contributed by Rajput-Ji
<script>
// JavaScript Program to implement
// the above approach
// Function to find the minimum number
// of intervals in the array A[] to
// cover the entire target interval
function minimizeSegment(A,
X)
{
// Sort the array A[] in increasing
// order of starting point
A.sort(function (a, b) { return a.first - b.first; })
// Insert a pair of INT_MAX to
// prevent going out of bounds
A.push({ first: Number.MAX_VALUE, second: Number.MAX_VALUE });
// Stores start of current interval
let start = X.first;
// Stores end of current interval
let end = X.first - 1;
// Stores the count of intervals
let cnt = 0;
// Iterate over all the intervals
for (let i = 0; i < A.length;) {
// If starting point of current
// index <= start
if (A[i].first <= start) {
end = Math.max(A[i++].second, end);
}
else {
// Update the value of start
start = end;
// Increment the value
// of count
++cnt;
// If the target interval is
// already covered or it is
// not possible to move
// then break the loop
if (A[i].first > end
|| end >= X.second) {
break;
}
}
}
// If the entire target interval
// is not covered
if (end < X.second) {
return -1;
}
// Return Answer
return cnt;
}
// Driver Code
let A = [{ first: 1, second: 3 },
{ first: 2, second: 4 },
{ first: 2, second: 10 },
{ first: 2, second: 3 },
{ first: 1, second: 1 }
];
let X = { first: 1, second: 10 };
document.write(minimizeSegment(A, X));
// This code is contributed by Potta Lokesh
</script>
Time Complexity: O(N*log N)
Auxiliary Space: O(1)
Efficient Approach:
The idea is similar to Minimum number of jumps to reach end. The tricky part is how to find the starting point to just cover the `target.first`. Basically, it is a Greedy question. We can use the "sweep line" like method to build an auxiliary array to mimic the Jump Game.
Implement the following steps to solve the problem:
- Initialize variables minVal to INT_MAX and maxVal to 0.
- Iterate over each interval i in A:
- Update minVal to the minimum of minVal and i.start.
- Update maxVal to the maximum of maxVal and i.end.
- Create a count array count of size (maxVal - minVal + 1) and initialize all elements to 0.
- Iterate over each interval i in A:
- Compute the index in the count array as i.start - minVal.
- Update count[i.start - minVal] to the maximum of count[i.start - minVal] and (i.end - i.start).
- Initialize variables reach and maxReach to 0.
- Compute the indices in the count array for the target interval as targetStart = X.first - minVal and targetEnd = X.second - minVal.
- Initialize a variable i to 0.
- Iterate while i is less than or equal to targetStart:
- If i + count[i] is less than targetStart, continue to the next iteration.
- Update reach to the maximum of reach and i + count[i].
- Increment i by 1.
- Initialize a variable res to 1.
- Continue iterating while i is less than the size of the count array:
- If reach is greater than or equal to targetEnd, break out of the loop.
- Update maxReach to the maximum of maxReach and i + count[i].
- If reach is less than or equal to i:
- Update reach to maxReach.
- Increment res by 1.
- Increment i by 1.
- If reach is greater than or equal to targetEnd, return res, otherwise return -1.
Below is the implementation of the approach:
C++
// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;
// Function to find the minimum number
// of intervals in the array A[] to
// cover the entire target interval
int minimizeSegment(vector<pair<int, int>> A, pair<int, int> X) {
// Check if the input vector is empty
if (A.empty())
return 0;
// Find the minimum and maximum values
int minVal = INT_MAX;
int maxVal = 0;
for (auto i : A) {
minVal = min(minVal, i.first);
maxVal = max(maxVal, i.second);
}
// Create a count array to store the length
// of intervals starting at each index
vector<int> count(maxVal - minVal + 1, 0);
for (auto i : A) {
count[i.first - minVal] = max(count[i.first - minVal], i.second - i.first);
}
// Initialize variables for tracking reach
int reach = 0;
int maxReach = 0;
int targetStart = X.first - minVal;
int targetEnd = X.second - minVal;
int i = 0;
// Iterate until reaching the target start
for (; i <= targetStart; i++) {
if (i + count[i] < targetStart)
continue;
reach = max(reach, i + count[i]);
}
// Initialize result and continue iteration
int res = 1;
for (; i < count.size(); i++) {
if (reach >= targetEnd)
break;
maxReach = max(maxReach, i + count[i]);
if (reach <= i) {
reach = maxReach;
res++;
}
}
// Check if the target interval is covered
return reach >= targetEnd ? res : -1;
}
int main() {
// Input intervals and target interval
vector<pair<int, int>> A = {
{1, 3}, {2, 4}, {2, 10}, {2, 3}, {1, 1}
};
pair<int, int> X = {1, 10};
// Find the minimum number of intervals
// to cover the target interval
int result = minimizeSegment(A, X);
cout << result << endl;
return 0;
}
// This code is contributed by Chandramani Kumar
import java.util.AbstractMap.SimpleEntry;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class Main {
// Function to find the minimum number of intervals to
// cover the target interval
public static int
minimizeSegment(List<SimpleEntry<Integer, Integer> > A,
SimpleEntry<Integer, Integer> X)
{
// Check if the input list is empty
if (A.isEmpty())
return 0;
// Find the minimum and maximum values
int minVal = Integer.MAX_VALUE;
int maxVal = 0;
for (SimpleEntry<Integer, Integer> interval : A) {
minVal = Math.min(minVal, interval.getKey());
maxVal = Math.max(maxVal, interval.getValue());
}
// Create a list to store the length of intervals
// starting at each index
List<Integer> count = new ArrayList<>(
Collections.nCopies(maxVal - minVal + 1, 0));
for (SimpleEntry<Integer, Integer> interval : A) {
count.set(interval.getKey() - minVal,
Math.max(count.get(interval.getKey()
- minVal),
interval.getValue()
- interval.getKey()));
}
// Initialize variables for tracking reach
int reach = 0;
int maxReach = 0;
int targetStart = X.getKey() - minVal;
int targetEnd = X.getValue() - minVal;
int i = 0;
// Iterate until reaching the target start
for (; i <= targetStart; i++) {
if (i + count.get(i) < targetStart)
continue;
reach = Math.max(reach, i + count.get(i));
}
// Initialize result and continue iteration
int res = 1;
for (; i < count.size(); i++) {
if (reach >= targetEnd)
break;
maxReach = Math.max(maxReach, i + count.get(i));
if (reach <= i) {
reach = maxReach;
res++;
}
}
// Check if the target interval is covered
return reach >= targetEnd ? res : -1;
}
public static void main(String[] args)
{
// Input intervals and target interval
List<SimpleEntry<Integer, Integer> > A
= new ArrayList<>();
A.add(new SimpleEntry<>(1, 3));
A.add(new SimpleEntry<>(2, 4));
A.add(new SimpleEntry<>(2, 10));
A.add(new SimpleEntry<>(2, 3));
A.add(new SimpleEntry<>(1, 1));
SimpleEntry<Integer, Integer> X
= new SimpleEntry<>(1, 10);
// Find the minimum number of intervals to cover the
// target interval
int result = minimizeSegment(A, X);
System.out.println(result);
}
}
# Function to find the minimum number
# of intervals in the array A[] to
# cover the entire target interval
def minimizeSegment(A, X):
# Check if the A is empty
if not A:
return 0
#Find minimum and maximum value
minVal = float('inf')
maxVal = 0
for i in A:
minVal = min(minVal, i[0])
maxVal = max(maxVal, i[1])
# Create array to store the length
# of interval starting at each index
count = [0] * (maxVal - minVal + 1)
for i in A:
count[i[0] - minVal] = max(count[i[0] - minVal], i[1] - i[0])
# Initializing variables for tracking reach
reach = 0
maxReach = 0
targetStart = X[0] - minVal
targetEnd = X[1] - minVal
i = 0
# Iterate until reaching the target start
while i <= targetStart:
if i + count[i] < targetStart:
i += 1
continue
reach = max(reach, i + count[i])
i += 1
# Initialize result and continue iteration
res = 1
while i < len(count):
if reach >= targetEnd:
break
maxReach = max(maxReach, i + count[i])
if reach <= i:
reach = maxReach
res += 1
i += 1
# check if the target interval is convered.
return res if reach >= targetEnd else -1
# Input intervals and target interval
A = [
(1, 3), (2, 4), (2, 10), (2, 3), (1, 1)
]
X = (1, 10)
result = minimizeSegment(A, X)
print(result)
using System;
using System.Collections.Generic;
using System.Linq;
class Program
{
// Function to find the minimum number
// of intervals in the list A to
// cover the entire target interval
static int MinimizeSegment(List<Tuple<int, int>> A, Tuple<int, int> X)
{
// Check if the input list is empty
if (A.Count == 0)
return 0;
// Find the minimum and maximum values
int minVal = int.MaxValue;
int maxVal = 0;
foreach (var interval in A)
{
minVal = Math.Min(minVal, interval.Item1);
maxVal = Math.Max(maxVal, interval.Item2);
}
// Create a count array to store the length
// of intervals starting at each index
List<int> count = new List<int>(maxVal - minVal + 1);
count.AddRange(Enumerable.Repeat(0, maxVal - minVal + 1));
foreach (var interval in A)
{
count[interval.Item1 - minVal] = Math.Max(count[interval.Item1 - minVal], interval.Item2 - interval.Item1);
}
// Initialize variables for tracking reach
int reach = 0;
int maxReach = 0;
int targetStart = X.Item1 - minVal;
int targetEnd = X.Item2 - minVal;
int i = 0;
// Iterate until reaching the target start
for (; i <= targetStart; i++)
{
if (i + count[i] < targetStart)
continue;
reach = Math.Max(reach, i + count[i]);
}
// Initialize result and continue iteration
int res = 1;
for (; i < count.Count; i++)
{
if (reach >= targetEnd)
break;
maxReach = Math.Max(maxReach, i + count[i]);
if (reach <= i)
{
reach = maxReach;
res++;
}
}
// Check if the target interval is covered
return reach >= targetEnd ? res : -1;
}
static void Main(string[] args)
{
// Input intervals and target interval
List<Tuple<int, int>> A = new List<Tuple<int, int>>
{
Tuple.Create(1, 3), Tuple.Create(2, 4), Tuple.Create(2, 10), Tuple.Create(2, 3), Tuple.Create(1, 1)
};
Tuple<int, int> X = Tuple.Create(1, 10);
// Find the minimum number of intervals
// to cover the target interval
int result = MinimizeSegment(A, X);
Console.WriteLine(result);
Console.ReadLine();
}
}
function minimizeSegment(A, X) {
// Check if the input vector is empty
if (A.length === 0)
return 0;
// Find the minimum and maximum values
let minVal = Infinity;
let maxVal = 0;
for (let i = 0; i < A.length; i++) {
minVal = Math.min(minVal, A[i][0]);
maxVal = Math.max(maxVal, A[i][1]);
}
// Create a count array to store the length
// of intervals starting at each index
let count = new Array(maxVal - minVal + 1).fill(0);
for (let i = 0; i < A.length; i++) {
count[A[i][0] - minVal] = Math.max(count[A[i][0] - minVal], A[i][1] - A[i][0]);
}
// Initialize variables for tracking reach
let reach = 0;
let maxReach = 0;
let targetStart = X[0] - minVal;
let targetEnd = X[1] - minVal;
let i = 0;
// Iterate until reaching the target start
for (; i <= targetStart; i++) {
if (i + count[i] < targetStart)
continue;
reach = Math.max(reach, i + count[i]);
}
// Initialize result and continue iteration
let res = 1;
for (; i < count.length; i++) {
if (reach >= targetEnd)
break;
maxReach = Math.max(maxReach, i + count[i]);
if (reach <= i) {
reach = maxReach;
res++;
}
}
// Check if the target interval is covered
return reach >= targetEnd ? res : -1;
}
// Input intervals and target interval
let A = [
[1, 3], [2, 4], [2, 10], [2, 3], [1, 1]
];
let X = [1, 10];
let result = minimizeSegment(A, X);
console.log(result);
Time Complexity: O(N) because single traversal is beeing done whether it is of array A or count.
Auxiliary Space: O(N) as count array has been created.
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Pattern SearchingPattern searching algorithms are essential tools in computer science and data processing. These algorithms are designed to efficiently find a particular pattern within a larger set of data. Patten SearchingImportant Pattern Searching Algorithms:Naive String Matching : A Simple Algorithm that works i
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GeometryGeometry is a branch of mathematics that studies the properties, measurements, and relationships of points, lines, angles, surfaces, and solids. From basic lines and angles to complex structures, it helps us understand the world around us.Geometry for Students and BeginnersThis section covers key br
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