Count of subarrays for each Array element in which arr[i] is first and least

Last Updated : 04 Apr, 2022

Given an array arr[], the task is to find the count of subarrays starting from the current element that has a minimum element as the current element itself.

Examples:

Input: arr[] = {2, 4, 2, 1, 3}
Output: {3, 1, 1, 2, 1}
Explanation: For the first element we can form 3 valid subarrays with the given condition

2 -> {2} , {2,4} , {2,4,2} = 3 subarrays and so on

4 -> {4} = 1 subarray

2 -> {2} = 1 subarray

1 -> {1} , {1, 3} = 2 subarrays

3 -> {3} = 1 subarray

Input: arr[] = {1, 4, 2, 5, 3}
Output: {5, 1, 3, 1, 1}

Naive Solution: The naive approach revolves around the idea that:

If smaller element is not found then count of subarrays = length of array – current index

If element is found then count of subarrays = index of smaller element – current index

The task can be solved using 2 loops. The outer loop picks all the elements one by one. The inner loop looks for the first smaller element for the element picked by the outer loop. If a smaller element is found then the index of that element – current index is stored as next, otherwise, the length – current index is stored.

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 count of subarrays
vector<int> countOfSubArray(vector<int> arr)
{
    int next, i, j;
    int n = arr.size();
    vector<int> ans;
 
    for (i = 0; i < n; i++) {
        bool flag = false;
 
        // If the next smaller element
        // is not found then
        // length - current index
        // would be the answer
        next = n - i;
        for (j = i + 1; j < n; j++) {
            if (arr[i] > arr[j]) {
 
                // If the next smaller
                // element is found then
                // the difference of indices
                // will be the count
                next = j - i;
                ans.push_back(next);
                flag = true;
                break;
            }
        }
 
        if (flag == false) {
            ans.push_back(next);
        }
    }
    return ans;
}
 
// Driver Code
int main()
{
    vector<int> arr{ 1, 4, 2, 5, 3 };
 
    vector<int> ans = countOfSubArray(arr);
 
    for (int i = 0; i < ans.size(); i++) {
        cout << ans[i] << " ";
    }
 
    return 0;
}

Java

// Java program for the above approach
import java.util.ArrayList;
 
class GFG {
 
  // Function to find the count of subarrays
  static ArrayList<Integer> countOfSubArray(int[] arr) {
    int next, i, j;
    int n = arr.length;
    ArrayList<Integer> ans = new ArrayList<Integer>();
 
    for (i = 0; i < n; i++) {
      boolean flag = false;
 
      // If the next smaller element
      // is not found then
      // length - current index
      // would be the answer
      next = n - i;
      for (j = i + 1; j < n; j++) {
        if (arr[i] > arr[j]) {
 
          // If the next smaller
          // element is found then
          // the difference of indices
          // will be the count
          next = j - i;
          ans.add(next);
          flag = true;
          break;
        }
      }
 
      if (flag == false) {
        ans.add(next);
      }
    }
    return ans;
  }
 
  // Driver Code
  public static void main(String args[])
  {
    int[] arr = { 1, 4, 2, 5, 3 };
    ArrayList<Integer> ans = countOfSubArray(arr);
 
    for (int i = 0; i < ans.size(); i++) {
      System.out.print(ans.get(i) + " ");
    }
  }
}
 
// This code is contributed by gfgking.

Python3

# Python code for the above approach
 
# Function to find the count of subarrays
def countOfSubArray(arr):
    n = len(arr)
    ans = []
 
    for i in range(n):
        flag = 0
 
        # If the next smaller element
        # is not found then
        # length - current index
        # would be the answer
        next = n - i
        for j in range(i + 1, n):
            if arr[i] > arr[j]:
 
                # If the next smaller
                # element is found then
                # the difference of indices
                # will be the count
                next = j - i
                ans.append(next)
                flag = 1
                break
 
        if flag == 0:
            ans.append(next)
 
    return ans
 
 # Driver Code
arr = [1, 4, 2, 5, 3]
ans = countOfSubArray(arr)
 
for i in range(len(ans)):
    print(ans[i], end = " ")
 
# This code is contributed by Potta Lokesh

C#

// C# program for the above approach
using System;
using System.Collections.Generic;
 
class GFG {
 
  // Function to find the count of subarrays
  static List<int> countOfSubArray(int[] arr)
  {
    int next, i, j;
    int n = arr.Length;
    List<int> ans = new List<int>();
 
    for (i = 0; i < n; i++) {
      bool flag = false;
 
      // If the next smaller element
      // is not found then
      // length - current index
      // would be the answer
      next = n - i;
      for (j = i + 1; j < n; j++) {
        if (arr[i] > arr[j]) {
 
          // If the next smaller
          // element is found then
          // the difference of indices
          // will be the count
          next = j - i;
          ans.Add(next);
          flag = true;
          break;
        }
      }
 
      if (flag == false) {
        ans.Add(next);
      }
    }
    return ans;
  }
 
  // Driver Code
  public static void Main()
  {
    int[] arr = { 1, 4, 2, 5, 3 };
    List<int> ans = countOfSubArray(arr);
 
    for (int i = 0; i < ans.Count; i++) {
      Console.Write(ans[i] + " ");
    }
  }
}
 
// This code is contributed by ukasp.

Javascript

<script>
    // JavaScript program for the above approach
 
    // Function to find the count of subarrays
    const countOfSubArray = (arr) => {
        let next, i, j;
        let n = arr.length;
        let ans = [];
 
        for (i = 0; i < n; i++) {
            let flag = false;
 
            // If the next smaller element
            // is not found then
            // length - current index
            // would be the answer
            next = n - i;
            for (j = i + 1; j < n; j++) {
                if (arr[i] > arr[j]) {
 
                    // If the next smaller
                    // element is found then
                    // the difference of indices
                    // will be the count
                    next = j - i;
                    ans.push(next);
                    flag = true;
                    break;
                }
            }
 
            if (flag == false) {
                ans.push(next);
            }
        }
        return ans;
    }
 
    // Driver Code
    let arr = [1, 4, 2, 5, 3];
    let ans = countOfSubArray(arr);
 
    for (let i = 0; i < ans.length; i++) {
        document.write(`${ans[i]} `);
    }
 
// This code is contributed by rakeshsahni
 
</script>

Output

5 1 3 1 1

Time Complexity: O(N²)
Auxiliary Space: O(1)

Efficient Solution: This problem basically asks to find how far is the current index from the index of the next smaller number to the number at the current index. The most optimal way to solve this problem is by making use of a stack.
Follow the below steps to solve the problem:

Iterate over each number of the given array arr[] using the current index.
If the stack is empty, push the current index to the stack.
If the stack is not empty then do the following:
- If the number at the current index is lesser than the number of the index at top of the stack, push the current index.
- If the number at the current index is greater than the number of the index at top of the stack, then update the count of subarrays as the index at top of the stack – current index
Pop the stack once the number of days has been updated in the output list.
Repeat the above steps for all the indices in the stack that are greater than the number at the current index.

Below is the implementation of the above approach:

C++

// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to determine how many count
// of subarrays are possible
// with each number
vector<int> countOfSubArray(vector<int> arr)
{
 
    stack<int> st;
    // To store the answer
    vector<int> v;
    int n = arr.size();
 
    // Traverse all the numbers
    for (int i = n - 1; i >= 0; i--) {
 
        // Check if current index is the
        // next smaller element of
        // any previous indices
        while (st.size() > 0 
               && arr[st.top()] >= arr[i]) {
            // Pop the element
            st.pop();
        }
 
        if (st.size() == 0) {
            v.push_back(n - i);
        }
        else {
            v.push_back(st.top() - i);
        }
 
        // Push the current index
        st.push(i);
    }
    // reverse the output
    reverse(v.begin(), v.end());
    return v;
}
 
// Driver Code
int main()
{
    // Given numbers
    vector<int> arr{ 1, 4, 2, 5, 3 };
 
    // Function Call
    vector<int> ans = countOfSubArray(arr);
 
    // Printing the result
    for (int i = 0; i < ans.size(); i++) {
        cout << ans[i] << " ";
    }
 
    return 0;
}

Java

// Java program for the above approach
import java.util.*;
class GFG{
 
// Function to determine how many count
// of subarrays are possible
// with each number
static Vector<Integer> countOfSubArray(int[] arr)
{
 
    Stack<Integer> st = new Stack<Integer>();
   
    // To store the answer
    Vector<Integer> v = new Vector<Integer>();
    int n = arr.length;
 
    // Traverse all the numbers
    for (int i = n - 1; i >= 0; i--) {
 
        // Check if current index is the
        // next smaller element of
        // any previous indices
        while (st.size() > 0
               && arr[st.peek()] >= arr[i])
        {
           
            // Pop the element
            st.pop();
        }
 
        if (st.size() == 0) {
            v.add(n - i);
        }
        else {
            v.add(st.peek() - i);
        }
 
        // Push the current index
        st.add(i);
    }
   
    // reverse the output
    Collections.reverse(v);
    return v;
}
 
// Driver Code
public static void main(String[] args)
{
   
    // Given numbers
    int []arr ={ 1, 4, 2, 5, 3 };
 
    // Function Call
    Vector<Integer> ans = countOfSubArray(arr);
 
    // Printing the result
    for (int i = 0; i < ans.size(); i++) {
        System.out.print(ans.get(i)+ " ");
    }
 
}
}
 
// This code is contributed by shikhasingrajput

Python3

# Python program for the above approach
 
# Function to determine how many count
# of subarrays are possible
# with each number
def countOfSubArray(arr):
    st = []
     
    # To store the answer
    v = []
    n = len(arr)
 
    # Traverse all the numbers
    for i in range(n - 1,-1,-1):
 
        # Check if current index is the
        # next smaller element of
        # any previous indices
        while len(st) > 0  and arr[st[len(st)-1]] >= arr[i] :
            # Pop the element
            st.pop()
 
        if (len(st) == 0):
            v.append(n - i)
        else:
            v.append(st[len(st) - 1]- i)
 
        # Push the current index
        st.append(i)
 
    # reverse the output
    v = v[::-1]
    return v
 
# Driver Code
 
# Given numbers
arr = [ 1, 4, 2, 5, 3 ]
 
# Function Call
ans = countOfSubArray(arr)
 
# Printing the result
for i in range(len(ans)):
    print(ans[i],end = " ")
     
# This code is contributed by shinjanpatra

C#

// C# program for the above approach
using System;
using System.Collections.Generic;
 
public class GFG{
 
  // Function to determine how many count
  // of subarrays are possible
  // with each number
  static List<int> countOfSubArray(int[] arr)
  {
 
    Stack<int> st = new Stack<int>();
 
    // To store the answer
    List<int> v = new List<int>();
    int n = arr.Length;
 
    // Traverse all the numbers
    for (int i = n - 1; i >= 0; i--) {
 
      // Check if current index is the
      // next smaller element of
      // any previous indices
      while (st.Count > 0 
             && arr[st.Peek()] >= arr[i])
      {
 
        // Pop the element
        st.Pop();
      }
 
      if (st.Count == 0) {
        v.Add(n - i);
      }
      else {
        v.Add(st.Peek() - i);
      }
 
      // Push the current index
      st.Push(i);
    }
 
    // reverse the output
    v.Reverse();
    return v;
  }
 
  // Driver Code
  public static void Main(String[] args)
  {
 
    // Given numbers
    int []arr ={ 1, 4, 2, 5, 3 };
 
    // Function Call
    List<int> ans = countOfSubArray(arr);
 
    // Printing the result
    for (int i = 0; i < ans.Count; i++) {
      Console.Write(ans[i]+ " ");
    }
  }
}
 
// This code is contributed by 29AjayKumar

Javascript

<script>
 
// JavaScript program for the above approach
 
// Function to determine how many count
// of subarrays are possible
// with each number
function countOfSubArray(arr)
{
 
    let st = [];
     
    // To store the answer
    let v = [];
    let n = arr.length;
 
    // Traverse all the numbers
    for (let i = n - 1; i >= 0; i--) {
 
        // Check if current index is the
        // next smaller element of
        // any previous indices
        while (st.length > 0 
               && arr[st[st.length-1]] >= arr[i])
        {
         
            // Pop the element
            st.pop();
        }
 
        if (st.length == 0) {
            v.push(n - i);
        }
        else {
            v.push(st[st.length - 1]- i);
        }
 
        // Push the current index
        st.push(i);
    }
     
    // reverse the output
    v.reverse();
    return v;
}
 
// Driver Code
 
// Given numbers
let arr = [ 1, 4, 2, 5, 3 ];
 
// Function Call
let ans = countOfSubArray(arr);
 
// Printing the result
for (let i = 0; i < ans.length; i++) {
    document.write(ans[i]," ");
}
 
// This code is contributed by shinjanpatra
 
</script>

Output

5 1 3 1 1

Time Complexity: O(N)
Auxiliary Space: O(N)

Count subarrays for every array element in which they are the minimum

prasanna1995

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Count of subarrays for each Array element in which arr[i] is first and least

C++

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Java

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