Leetcode 370. Range Addition

Assume you have an array of length n initialized with all 0's and are given k update operations.

Each operation is represented as a triplet: [startIndex, endIndex, inc] which increments each element of subarray A[startIndex ... endIndex] (startIndex and endIndex inclusive) with inc.

Return the modified array after all k operations were executed.

Example:

Given:

    length = 5,
    updates = [
        [1,  3,  2],
        [2,  4,  3],
        [0,  2, -2]
    ]

Output:

    [-2, 0, 3, 5, 3]

Explanation:

Initial state:
[ 0, 0, 0, 0, 0 ]

After applying operation [1, 3, 2]:
[ 0, 2, 2, 2, 0 ]

After applying operation [2, 4, 3]:
[ 0, 2, 5, 5, 3 ]

After applying operation [0, 2, -2]:
[-2, 0, 3, 5, 3 ]

Credits:
Special thanks to @vinod23 for adding this problem and creating all test cases.

Code (Java):

class Solution {
    public int[] getModifiedArray(int length, int[][] updates) {
        int[] ans = new int[length];
        
        for (int[] update : updates) {
            int start = update[0];
            int end = update[1];
            int inc = update[2];
            
            ans[start] += inc;
            if (end + 1 < length) {
                ans[end + 1] += -inc;
            }
        }

        for (int i = 1; i < length; i++) {
            ans[i] += ans[i -1];
        }
        
        return ans;
    }
}

Analysis:
Time complexity: O(n + k), where n is the length, and k is the number of update operations.