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.

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More practice:

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

思路：对于每个元素，有两种情况，要么前面的和与它相加比它还小，那就从它另起一组继续往后加；如果加上它后比他大，则可以继续累加。同时用一个全局变量保存当前最大值。注意这里不是只要和增大就继续加，因为是要找到最大的子序列的和，所以强调最大。

class Solution {public:    int maxSubArray(int A[], int n) {        if (n == 0) {            return 0;        }                vector<int> sum(n, 0);        sum[0] = A[0];        int result = A[0];                for (int i = 1; i < n; i++) {            sum[i] = max(A[i], sum[i-1] + A[i]);            result = max(result, sum[i]);        }                return result;    }};