# 724.Find Pivot Index

**724.Find Pivot Index**

难度:Easy

> 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.
 

Note:

The length of nums will be in the range [0, 10000].
Each element nums[i] will be an integer in the range [-1000, 1000].
```

找到一条平分轴，使得左右两边和相等。可以先求出总和，然后从左开始递增，每次比较左边的和与总和减去轴上的值的一半是否相等，相等则返回轴的索引。

```
class Solution {
public:
    int pivotIndex(vector<int>& nums) {
        if(nums.empty()) return -1;
        int sum= accumulate(nums.begin(),nums.end(),0);
        int leftSum=0;
        for(int index=0;index<nums.size();index++)
        {
            int tmp=sum-nums[index];
            if(tmp%2 ==0 && leftSum ==tmp/2)
                return index;
             leftSum += nums[index];

    }
        return -1;
    }
};
```

> 执行用时 :28 ms, 在所有 C++ 提交中击败了85.29%的用户\
> 内存消耗 :9.8 MB, 在所有 C++ 提交中击败了89.77%的用户


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://dfine.gitbook.io/leetcode/724.find_pivot_index.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.