Replace Elements with Greatest Element on Right Side

Description

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]

Constraints:

• 1 <= arr.length <= 10^4

• 1 <= arr[i] <= 10^5

Code

// 从后向前求，向前移动一个单位时，只需要判断新增的数和原来最大值的大小
public int[] replaceElements(int[] arr) {
    int maxNum = arr[arr.length - 1];
    int t = arr[arr.length - 1];
    arr[arr.length - 1] = -1;
    for (int i = arr.length - 2; i >= 0; i--) {
        maxNum = Math.max(maxNum, t);
        t = arr[i];
        arr[i] = maxNum;
    }
    return arr;
}