[copy title]:
Given an array of integers nums, write a method that returns the "pivot" index of this array.
We define the pivot index as the index where the sum of the numbers to the left of the index is equal to the sum of the numbers to the right of the index.
If no such index exists, we should return -1. If there are multiple pivot indexes, you should return the left-most pivot index.
Example 1:
Input: nums = [1, 7, 3, 6, 5, 6] Output: 3 Explanation: The sum of the numbers to the left of index 3 (nums[3] = 6) is equal to the sum of numbers to the right of index 3. Also, 3 is the first index where this occurs.
Example 2:
Input: nums = [1, 2, 3] Output: -1 Explanation: There is no index that satisfies the conditions in the problem statement.
[brute force solution]:
Both leftsum and rightsum use for loop to find
Time analysis: n+n
Space Analysis:
[After optimization]: Find leftsum, and use subtraction to determine whether sum - nums[i] - leftsum is equal to leftsum
Time analysis: n+1
Space Analysis:
[Wonderful output conditions]:
[Wonderful corner case]:
[Thinking question]:
[One sentence idea]:
Convert addition to subtraction to reduce time complexity
[Input amount]: Empty: Normal situation: Extra large: Extra small: Special situations handled in the program: Abnormal situations (Illegal and unreasonable input):
[Paint]:
[One brush]:
[Second brush]:
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[Results of five-minute naked eye debug]:
[Summarize]:
[Complexity]: Time complexity: O( ) Space complexity: O( )
[English data structures or algorithms, why not use other data structures or algorithms]:
[Key templating code]:
[Other solutions]:
［Follow Up］：
[The topics given by LC change and change]:
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