[LeetCode] Range Addition 范围相加 - 博客吧

[LeetCode] Range Addition 范围相加 - 博客吧

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 ] 

Hint:

1. Thinking of using advanced data structures? You are thinking it too complicated.
2. For each update operation, do you really need to update all elements between i and j?
3. Update only the first and end element is sufficient.
4. The optimal time complexity is O(k + n) and uses O(1) extra space.

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

 

这道题刚添加的时候我就看到了，当时只有1个提交，0个接受，于是我赶紧做，提交成功后发现我是第一个提交成功的，哈哈，头一次做沙发啊，有点小激动~这道题的提示说了我们肯定不能把范围内的所有数字都更新，而是只更新开头结尾两个数字就行了，那么我们的做法就是在开头坐标startIndex位置加上inc，而在结束位置加1的地方加上-inc，那么根据题目中的例子，我们可以得到一个数组，nums = {-2, 2, 3, 2, -2, -3}，然后我们发现对其做累加和就是我们要求的结果result = {-2, 0, 3, 5, 3}，参见代码如下：

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