求数组的最大子段和，动态规划 时间复杂度O(n)

int MaxSum(int *a,int n,int &besti,int &bestj){int b = 0;int maxsum = 0;besti = 1;bestj = 1;for (int i = 1; i <= n; ++i){if(b < 0){b = a[i];besti = i;}elseb += a[i];if(b > maxsum){maxsum = b;bestj = i;}}return maxsum;}