370 Range Addition

370. Range Addition

1. Question

Assume you have an array of lengthninitialized with all0's and are given k update operations.

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

Return the modified array after allkoperations 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 ]

2. Implementation

思路: https://leetcode.com/problems/range-addition/discuss/84225/Detailed-explanation-if-you-don't-understand-especially-%22put-negative-inc-at-endIndex+1%22

class Solution {
    public int[] getModifiedArray(int length, int[][] updates) {
        int[] res = new int[length];

        for (int[] update : updates) {
            int start = update[0];
            int end = update[1];
            int value = update[2];

            res[start] += value;
            if (end + 1 < length) {
                res[end + 1] -= value;
            }
        }

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

3. Time & Space Complexity

时间复杂度O(n + k), 空间复杂度O(n)