53. [LeetCode] Maximum Subarray

Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.

Example:

Input: [-2,1,-3,4,-1,2,1,-5,4],
Output: 6
Explanation: [4,-1,2,1] has the largest sum = 6.

Follow up:

If you have figured out the O(n) solution, try coding another solution using the divide and conquer approach, which is more subtle.

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方法一：不过这个方法对全是负数时，不成立；

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class Solution {
public:
    int maxSubArray(vector<int>& nums) {
        int ans=nums[0],sum=0;
        for(int i=0; i<nums.size();i++){
          sum+=nums[i];
          ans=max(ans,sum);
           sum=max(sum,0);
        }
      return ans;  
    }
};

//Idea is very simple. Basically, keep adding each integer to the sequence until the sum drops below 0.
//If sum is negative, then should reset the sequence.