LeetCode 1013. 将数组分成和相等的三个部分

class Solution {
public:
    bool canThreePartsEqualSum(vector<int>& A) {
        int sum = 0, i;
        for(i = 0; i < A.size(); ++i)
        	sum += A[i];
        if(sum%3 )
        	return false;//不能整除3，错
        int part1of3 = sum/3;
        sum = 0;
        bool cut1 = false, cut2 = false;
        for(i = 0; i < A.size()-1; ++i)//注意size-1，留一个至少【-1,1,-1,1】
        {
        	sum += A[i];
        	if(sum == part1of3 && !cut1)//刚好等于1/3
        	{
        		cut1 = true;//第一刀切一下
        		sum = 0;//sum归0
        	}
        	else if(sum == part1of3 && cut1)//刚好等于1/3，且第一刀已切
        		return true;
        }
        return false;
    }
};