快樂的LeetCode --- 面試題42. 連續子數組的最大和

題目描述：

輸入一個整型數組，數組裏有正數也有負數。數組中的一個或連續多個整數組成一個子數組。求所有子數組的和的最大值。

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解題思路1: 超出時間限制

最容易能想到的思路，莫過於兩個for循環

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代碼1：

class Solution(object):
    def maxSubArray(self, nums):
        size = len(nums)
        max_num = max(nums)
        for i in range(size):
            for j in range(i+1, size+1):
                if max_num < sum(nums[i:j]):
                    max_num = sum(nums[i:j])
        return max_num

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解題思路2: 來源於官方

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代碼2：

class Solution(object):
    def maxSubArray(self, nums):
        dp = []
        dp.append(nums[0])
        for i in range(1, len(nums)):
            if dp[i-1] <= 0:
                dp.append(nums[i])
            else: 
                dp.append(dp[i-1] + nums[i])  
        return max(dp)

官方代碼：

class Solution:
    def maxSubArray(self, nums: List[int]) -> int:
        for i in range(1, len(nums)):
            nums[i] += max(nums[i - 1], 0)
        return max(nums)

C++解法：

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

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題目來源：

https://leetcode-cn.com/problems/lian-xu-zi-shu-zu-de-zui-da-he-lcof/