LeetCode53. 最大子序和（分治）

题目链接：Leetcode53

Code：

class Solution {
public:
    int maxSubArray(vector<int>& nums) {
        if (nums.size() == 0) return 0;
        return dfs(nums, 0, nums.size()-1);   
    }
    int dfs(vector<int>& num, int l, int r) {
        if (l == r) return num[l];
        return max(dfs(num, l, l+(r-l>>1)), max(dfs(num, l+(r-l>>1)+1, r), f(num, l, r)));
    }
    int f(vector<int>& num, int l, int r) {
        int m = l+(r-l>>1);
        int ls, rs;
        ls = rs = 1<<31;
        int s = 0;
        for(int i=m; i>=l; i--) {
            s += num[i];
            ls=max(s, ls);
        }
        s = 0;
        for (int i=m+1; i<=r; i++) {
            s += num[i];
            rs=max(s, rs);
        }
        return rs+ls;
    }
};