1299. Replace Elements with Greatest Element on Right Side

Problem

Tags: Array

Given an array arr, replace every element in that array with the greatest element among the elements to its right, and replace the last element with -1.

After doing so, return the array.

Example 1:

Input: arr = [17,18,5,4,6,1]
Output: [18,6,6,6,1,-1]
Explanation: 
- index 0 --> the greatest element to the right of index 0 is index 1 (18).
- index 1 --> the greatest element to the right of index 1 is index 4 (6).
- index 2 --> the greatest element to the right of index 2 is index 4 (6).
- index 3 --> the greatest element to the right of index 3 is index 4 (6).
- index 4 --> the greatest element to the right of index 4 is index 5 (1).
- index 5 --> there are no elements to the right of index 5, so we put -1.

Example 2:

Input: arr = [400]
Output: [-1]
Explanation: There are no elements to the right of index 0.

Constraints:

• 1 <= arr.length <= 10^4
• 1 <= arr[i] <= 10^5

Code

C

// 1299. Replace Elements with Greatest Element on Right Side (1/8/54028)
// Runtime: 98 ms (45.25%) Memory: 12.35 MB (70.95%) 

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* replaceElements(int arr[], int arrSize, int* returnSize) {
    int max = arr[arrSize - 1];
    arr[arrSize - 1] = -1;
    
    for (int i = arrSize - 2; i >= 0; i--) {
        if (arr[i] <= max) {
            arr[i] = max;
        } else {
            int tmp = max;
            max = arr[i];
            arr[i] = tmp;
        }
    }
    
    *returnSize = arrSize;
    return arr;
}