370 Range Addition
Problem:
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.
Hint: Thinking of using advanced data structures? You are thinking it too complicated. For each update operation, do you really need to update all elements between i and j? Update only the first and end element is sufficient. The optimal time complexity is O(k + n) and uses O(1) extra space.
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 ]
public class Solution {
public int[] getModifiedArray(int length, int[][] updates) {
int[] result = new int[length];
for (int i = 0; i < updates.length; i ++) {
result[updates[i][0]] += updates[i][2];
if (updates[i][1] + 1 < length) {
result[updates[i][1] + 1] -= updates[i][2];
}
}
int curr = 0;
for (int i = 0; i < result.length; i ++) {
if (result[i] != 0) {
curr += result[i];
}
result[i] = curr;
}
return result;
}
}