9---LeetCode【Maximum Subarray】|C語言|

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.

O(N^2) 解法：

int maxSubArray(int* nums, int numsSize) {
   
    int max = nums[0];
    int sum = 0;
    for (int i = 0; i < numsSize; i++) {
        sum = 0;
        for (int j = i; j < numsSize; j++) {
            sum += nums[j];
            if (max < sum) max = sum;
        }
    }
    return max;
}

O(N)解法：

int maxSubArray(int* nums, int numsSize) {
   
    int max = nums[0];
    int local = nums[0];
    for (int i = 1; i < numsSize; i++) {
        local = (local > 0)? local + nums[i]: nums[i];
        max = (max < local)? local: max;
    }
    return max;
}

分析：

1. 分爲兩個部分，local和max

2. local如果小於等於0，那麼就截斷，繼續往後找

3. max寄存已經找到的最大值