Maximum Subarray

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.

click to show more practice.

More practice:

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

 1 public class Solution {

 2     public int maxSubArray(int[] A) {

 3         // Note: The Solution object is instantiated only once and is reused by each test case.

 4         int sum = 0;

 5         int max = Integer.MIN_VALUE;

 6         if(A == null) return 0;

 7         int len = A.length;

 8         if(len == 0) return 0;

 9         for(int i = 0; i < len; i ++)

10         {

11             sum += A[i];

12             if(sum > max) max = sum;

13             if(sum < 0) sum = 0;

14         }

15         return max;

16     }

17 }

这一题做了太多次了。。。。

 

第三遍：

 1 public class Solution {

 2     public int maxSubArray(int[] A) {

 3         if(A == null || A.length == 0) return 0;

 4         int pre = 0, sum = 0, max = Integer.MIN_VALUE;

 5         while(pre < A.length){

 6             if(sum >= 0){

 7                 sum += A[pre ++];

 8                 max = max > sum ? max : sum;

 9             }else

10                 sum = 0;

11         }

12         return max;

13     }

14 }