Leetcode|简单|区间贪心|42/53. 最大子序和（暴力+贪心+动规）

class Solution {
public:
    int maxSubArray(vector<int>& nums) {
        int maxSum = INT_MIN;
        for (int i = 0; i < nums.size(); i++) {
            int sum = 0;
            int curSum = INT_MIN;
            for (int j = i; j < nums.size(); j++) {
                sum += nums[j];
                curSum = max(curSum, sum);
            }
            maxSum = max(maxSum, curSum);
        }
        return maxSum;
    }
};

class Solution {
public:
    int maxSubArray(vector<int>& nums) {
        int maxSum = INT_MIN;
        int curSum = 0;  // 当前区间中的和
        for (int i = 0; i < nums.size(); i++) {
            curSum += nums[i];
            maxSum = max(maxSum, curSum);
            // 核心：若之前的curSum为负数, 则置0, 因为前面的负数和一定会拉低后面的正和(全负数也满足)
            curSum = max(curSum, 0);  // 修正最大和的起始位置
        }
        return maxSum;
    }
};

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