MaximumSubarray

problem

Maximum Subarray

Easy

Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.

Example:

1
2
3
4
> Input: [-2,1,-3,4,-1,2,1,-5,4],
> Output: 6
> Explanation: [4,-1,2,1] has the largest sum = 6.
>

Follow up:

If you have figured out the O(n) solution, try coding another solution using the divide and conquer approach, which is more subtle.

key

我们定义一个和为第一位数,然后用curSum来保存递增量

ps ans–>answer cur–>cursor

solution

1
2
3
4
5
6
7
8
9
10
11
12
13
class Solution {
public int maxSubArray(int[] nums) {
int ans=nums[0], curSum=0;

for (int i=0; i<nums.length; i++) {
curSum = curSum + nums[i];
ans = Math.max(ans, curSum);
curSum = Math.max(0, curSum);
}

return ans;
}
}

perfect

1
2
3
4
5
6
7
8
9
10
class Solution {
public int maxSubArray(int[] nums) {
int dp = nums[0], maxSum=nums[0];
for (int i=1; i<nums.length; i++) {
dp = dp<0?nums[i]:nums[i]+dp;
maxSum=Math.max(maxSum, dp);
}
return maxSum;
}
}