MaxSubArray 最大子数列和

1 public int maxSubArray(int[] A) {

2            int newsum=A[0];

3            int max=A[0];

4            for(int i=1;i<A.length;i++){

5                newsum=Math.max(newsum+A[i],A[i]);

6                max= Math.max(max, newsum);

7            }

8            return max;

9         }

 

 

 1 int maxSubArray(int *a, const int length) 

 2 { 

 3     int maxSumSubArray = 0; 

 4     int sum_i = 0;  

 5     for(int i=0; i <length; i++) 

 6     { 

 7        sum_i = sum_i + a[i]; 

 8        if(sum_i < 0) sum_i = 0; 

 9         else 

10         { 

11             if(sum_i > maxSumSubArray) maxSumSubArray = sum_i; 

12         } 

13     } 

14  

15     //若是数组中的元素均为负值 

16     if(sum_i==0) 

17     { 

18         for(int i=0; i < length; i++) 

19         { 

20             if(a[i] > maxSumSubArray) maxSumSubArray = a[i]; 

21         } 

22     }    

23     return maxSumSubArray;     

24 } 

 

还有一种是分治算法 自己写的 复杂度O（nlogn）

 1 #include<iostream>

 2 using namespace std;

 3 int MaxSubArray(int *A,int low,int high){

 4     if(low==high) return A[low];

 5     int mid=(low+high)/2;

 6     int maxl=MaxSubArray(A,low,mid);

 7     int maxr=MaxSubArray(A,mid+1,high);

 8     int maxleft=A[mid],maxright=A[mid+1],maxsum;

 9     maxsum=A[mid];

10     if(mid-1>=low)

11     for(int i=mid-1;i>=low;i--){

12         maxsum=maxsum+A[i];

13         maxleft=max(maxsum,maxleft);

14     } 

15     maxsum=A[mid+1];

16     if(mid+2<=high)

17     for(int i=mid+2;i<=high;i++){

18         maxsum=maxsum+A[i];

19         maxright=max(maxsum,maxright);

20     } 

21     int cross=maxleft+maxright;

22     return max(cross,max(maxl,maxr));

23     

24 }

25 int main(){

26     int a[]={1,-4,1,3,-4,2};

27     cout<<MaxSubArray(a,0,5)<<endl;

28     return 0;

29 }