分治法和动态规划法解最大子序列问题 C++

分治法：

class Solution {public:    int maxCross(int A[], int low, int high)    {        int mid = (low + high)/2;        int leftsum = A[mid];        int sum = 0;        for (int i = mid; i >= low; i--)        {            sum = sum + A[i];            if (sum > leftsum)                leftsum = sum;        }        int rightsum = A[mid+1];        sum = 0;        for (int j = mid+1; j <= high; j++)        {            sum = sum + A[j];            if (sum > rightsum)                rightsum = sum;        }        return (rightsum + leftsum);                 }    int maxFind(int A[], int low, int high)    {        int mid;        if (low == high)            return A[low];        else        {            mid = (low + high)/2;            int left,right, cross;            left = maxFind(A, low, mid);            right = maxFind(A, mid+1, high);            cross = maxCross(A, low, high);            return max(max(left,right), cross);        }    }    int maxSubArray(int A[], int n) {        int sum;        sum = maxFind(A, 0, n-1);        return sum;    }};

动态规划法：

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