【leetcode】53. Maximum Subarray

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本文介绍了一种寻找数组中连续子数组并求其最大和的算法实现。以示例[-2,1,-3,4,-1,2,1,-5,4]为例，详细阐述了递归算法的过程，最终找出[4,-1,2,1]作为具有最大和6的子数组。

53. Maximum Subarray
Find the contiguous subarray within an array (containing at least one number) which has the largest sum.

For example, given the array [−2,1,−3,4,−1,2,1,−5,4],
the contiguous subarray [4,−1,2,1] has the largest sum = 6.

class Solution {
public:
    int maxSubArray(vector<int>& nums) {
        return maxSubArrayHelp(nums,0,nums.size()-1);
    }

    int maxSubArrayHelp(vector<int>& nums,int begin, int end){
        if(begin>end){
            return INT_MIN;
        }
        if(begin==end){
            return nums[begin];
        }
        int mid = (begin+end)/2;
        int leftMax = maxSubArrayHelp(nums,begin,mid-1);
        int rightMax = maxSubArrayHelp(nums,mid+1,end);

        int lMax=0;
        int left = 0;
        for(int i=mid-1;i>=begin;i--){
            left = left+nums[i];
            lMax = max(left,lMax);
        }

        int rMax = 0;
        int right =0;
        for(int i=mid+1;i<=end;i++){
            right = right+nums[i];
            rMax = max(right,rMax);
        }
        return max(lMax+rMax+nums[mid],max(leftMax,rightMax));
    }
};