724. Find Pivot Index(找基准--左右和相等)

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].

 public int pivotIndex(int[] nums) {
    int sum=0;int leftSum=0;
     for(int i=0;i!=nums.length;i++){
         sum+=nums[i];
     }

     for(int i=0;i!=nums.length;i++){
         if(i>0) leftSum+=nums[i-1];
         if(sum-nums[i]-leftSum==leftSum) return i;
     }
     return -1;

 }
;