LeetCode 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.

 

题目要求最大连续子数组的和，这里比较直接的思路是用动态规划，利用分治思想把问题进行拆分，我们用两个变量分别记录当前和与最大和，如果当前和是负数，那么就可以把它舍弃直接用数组中的当前数字代替它即可，因为负数加上之后当前数字比当前数字更小，不如不加，代码如下：

class Solution {
public:
    int maxSubArray(vector<int>& nums) 
    {
        int nCurSum = 0;           //当前和
        int nGreatestSum = INT_MIN;  //最大和
        for (auto num : nums)
        {
            nCurSum = max(num, num + nCurSum);
            nGreatestSum = max(nCurSum, nGreatestSum);
        }
        return nGreatestSum;
    }
};

或者是不调用max函数，但是这样做并不能提高速度：

class Solution {
public:
    int maxSubArray(vector<int>& nums) 
    {
        int nCurSum = 0;
        int nGreatestSum = INT_MIN;
        for (auto num : nums)
        {
            if (nCurSum <= 0)
                nCurSum = num;
            else
                nCurSum += num;
            if (nCurSum > nGreatestSum)
                nGreatestSum = nCurSum;
        }
        return nGreatestSum;
    }
};