Java Program to Find element at given index after a number of rotations
Last Updated :
23 May, 2022
An array consisting of N integers is given. There are several Right Circular Rotations of range[L..R] that we perform. After performing these rotations, we need to find element at a given index.
Examples :
Input : arr[] : {1, 2, 3, 4, 5}
ranges[] = { {0, 2}, {0, 3} }
index : 1
Output : 3
Explanation : After first given rotation {0, 2}
arr[] = {3, 1, 2, 4, 5}
After second rotation {0, 3}
arr[] = {4, 3, 1, 2, 5}
After all rotations we have element 3 at given
index 1.
Method : Brute-force The brute force approach is to actually rotate the array for all given ranges, finally return the element in at given index in the modified array.
Method : Efficient We can do offline processing after saving all ranges.
Suppose, our rotate ranges are : [0..2] and [0..3]
We run through these ranges from reverse.
After range [0..3], index 0 will have the element which was on index 3.
So, we can change 0 to 3, i.e. if index = left, index will be changed to right.
After range [0..2], index 3 will remain unaffected.
So, we can make 3 cases :
If index = left, index will be changed to right.
If index is not bounds by the range, no effect of rotation.
If index is in bounds, index will have the element at index-1.
Below is the implementation :
For better explanation:-
10 20 30 40 50
Index: 1
Rotations: {0,2} {1,4} {0,3}
Answer: Index 1 will have 30 after all the 3 rotations in the order {0,2} {1,4} {0,3}.
We performed {0,2} on A and now we have a new array A1.
We performed {1,4} on A1 and now we have a new array A2.
We performed {0,3} on A2 and now we have a new array A3.
Now we are looking for the value at index 1 in A3.
But A3 is {0,3} done on A2.
So index 1 in A3 is index 0 in A2.
But A2 is {1,4} done on A1.
So index 0 in A2 is also index 0 in A1 as it does not lie in the range {1,4}.
But A1 is {0,2} done on A.
So index 0 in A1 is index 2 in A.
On observing it, we are going deeper into the previous rotations starting from the latest rotation.
{0,3}
|
{1,4}
|
{0,2}
This is the reason we are processing the rotations in reverse order.
Please note that we are not rotating the elements in the reverse order, just processing the index from reverse.
Because if we actually rotate in reverse order, we might get a completely different answer as in case of rotations the order matters.
Java
import java.util.*;
class GFG
{
static int findElement(int[] arr, int[][] ranges,
int rotations, int index)
{
for (int i = rotations - 1; i >= 0; i--) {
int left = ranges[i][0];
int right = ranges[i][1];
if (left <= index && right >= index) {
if (index == left)
index = right;
else
index--;
}
}
return arr[index];
}
public static void main (String[] args) {
int[] arr = { 1, 2, 3, 4, 5 };
int rotations = 2;
int[][] ranges = { { 0, 2 }, { 0, 3 } };
int index = 1;
System.out.println(findElement(arr, ranges,
rotations, index));
}
}
|
Output :
3
Time Complexity: O(N), where N represents the given number of rotations.
Auxiliary Space: O(1), no extra space is required, so it is a constant.
Please refer complete article on Find element at given index after a number of rotations for more details!
Similar Reads
Java Program to Generate all rotations of a number
Given an integer n, the task is to generate all the left shift numbers possible. A left shift number is a number that is generated when all the digits of the number are shifted one position to the left and the digit at the first position is shifted to the last.Examples: Input: n = 123 Output: 231 31
2 min read
Java Program to Find the Mth element of the Array after K left rotations
Given non-negative integers K, M, and an array arr[] with N elements find the Mth element of the array after K left rotations. Examples: Input: arr[] = {3, 4, 5, 23}, K = 2, M = 1Output: 5Explanation:Â The array after first left rotation a1[ ] = {4, 5, 23, 3}The array after second left rotation a2[ ]
3 min read
Java Program to Rotate digits of a given number by K
Given two integers N and K, the task is to rotate the digits of N by K. If K is a positive integer, left rotate its digits. Otherwise, right rotate its digits. Examples: Input: N = 12345, K = 2Output: 34512 Explanation: Left rotating N(= 12345) by K(= 2) modifies N to 34512. Therefore, the required
2 min read
Java Program to Maximize count of corresponding same elements in given Arrays by Rotation
Given two arrays arr1[] and arr2[] of N integers and array arr1[] has distinct elements. The task is to find the maximum count of corresponding same elements in the given arrays by performing cyclic left or right shift on array arr1[]. Examples:  Input: arr1[] = { 6, 7, 3, 9, 5 }, arr2[] = { 7, 3,
3 min read
Java Program to Find Maximum value possible by rotating digits of a given number
Given a positive integer N, the task is to find the maximum value among all the rotations of the digits of the integer N. Examples: Input: N = 657Output: 765Explanation: All rotations of 657 are {657, 576, 765}. The maximum value among all these rotations is 765. Input: N = 7092Output: 9270Explanati
2 min read
Java Program to Find the Index of the TreeSet Element
Unlike the List classes like ArrayList or a LinkedList, the TreeSet class does not allow accessing elements using the index. There are no direct methods to access the TreeSet elements using the index and thus finding an index of an element is not straightforward. Methods: There are primarily three s
6 min read
Java Program to Rotate bits of a number
Bit Rotation: A rotation (or circular shift) is an operation similar to a shift except that the bits that fall off at one end are put back to the other end. In the left rotation, the bits that fall off at the left end are put back at the right end. In the right rotation, the bits that fall off at th
3 min read
Java Program to Modify given array to a non-decreasing array by rotation
Given an array arr[] of size N (consisting of duplicates), the task is to check if the given array can be converted to a non-decreasing array by rotating it. If it's not possible to do so, then print "No". Otherwise, print "Yes". Examples: Input: arr[] = {3, 4, 5, 1, 2}Output: YesExplanation:Â After
2 min read
Java Program for Find the element that appears once
Given an array where every element occurs three times, except one element which occurs only once. Find the element that occurs once. Expected time complexity is O(n) and O(1) extra space. Examples : Input: arr[] = {12, 1, 12, 3, 12, 1, 1, 2, 3, 3} Output: 2 In the given array all element appear thre
2 min read
Find Mth element after K Right Rotations of an Array
Given non-negative integers K, M, and an array arr[ ] consisting of N elements, the task is to find the Mth element of the array after K right rotations. Examples: Input: arr[] = {3, 4, 5, 23}, K = 2, M = 1 Output: 5 Explanation: The array after first right rotation a1[ ] = {23, 3, 4, 5} The array a
11 min read