LeetCode 53. 最大子序和

题目描述：

解法一（DP）：

class Solution {
public:
    int maxSubArray(vector<int>& nums) {
        if(nums.size()==1) return  nums[0];
        int res=nums[0],temp=nums[0];
        for(int i=1;i<nums.size();i++){
            if(temp<=0)
                temp=nums[i];
            else temp+=nums[i];
            res=max(res,temp);
        }
        return res;
    }
};

解法二（分治）：

class Solution {
    //分治算法
    private int divide(int[] nums, int left, int right){
        if(left == right) return nums[left];
        if(left == right - 1){
            int max;
            max = Math.max(nums[left], nums[right]);
            max = Math.max(max, nums[left] + nums[right]);
            return max;
        }

        int mid  = (left + right) >> 1;
        int lSum = divide(nums, left, mid - 1);
        int rSum = divide(nums, mid + 1, right);

        int max = nums[mid];
        int sum = max;
        for(int i = mid - 1; i >= left; i--){
            sum += nums[i];
            max = Math.max(max, sum);
        }

        sum = max;
        for(int j = mid + 1; j <= right; j++){
            sum += nums[j];
            max = Math.max(max, sum);
        }

        max = Math.max(max, lSum);
        max = Math.max(max, rSum);
        return max; 
    }
    public int maxSubArray(int[] nums) {
        return divide(nums, 0, nums.length-1);
    }
}