MaxSubArray 最大子数列和

public int maxSubArray(int[] A) {
           int newsum=A[0];
           int max=A[0];
           for(int i=1;i<A.length;i++){
               newsum=Math.max(newsum+A[i],A[i]);
               max= Math.max(max, newsum);
           }
           return max;
        }

int maxSubArray(int *a, const int length) 
{ 
    int maxSumSubArray = 0; 
    int sum_i = 0;  
    for(int i=0; i <length; i++) 
    { 
       sum_i = sum_i + a[i]; 
       if(sum_i < 0) sum_i = 0; 
        else 
        { 
            if(sum_i > maxSumSubArray) maxSumSubArray = sum_i; 
        } 
    } 
 
    //若是数组中的元素均为负值 
    if(sum_i==0) 
    { 
        for(int i=0; i < length; i++) 
        { 
            if(a[i] > maxSumSubArray) maxSumSubArray = a[i]; 
        } 
    }    
    return maxSumSubArray;     
} 

还有一种是分治算法 自己写的 复杂度O（nlogn）

#include<iostream>
using namespace std;
int MaxSubArray(int *A,int low,int high){
    if(low==high) return A[low];
    int mid=(low+high)/2;
    int maxl=MaxSubArray(A,low,mid);
    int maxr=MaxSubArray(A,mid+1,high);
    int maxleft=A[mid],maxright=A[mid+1],maxsum;
    maxsum=A[mid];
    if(mid-1>=low)
    for(int i=mid-1;i>=low;i--){
        maxsum=maxsum+A[i];
        maxleft=max(maxsum,maxleft);
    } 
    maxsum=A[mid+1];
    if(mid+2<=high)
    for(int i=mid+2;i<=high;i++){
        maxsum=maxsum+A[i];
        maxright=max(maxsum,maxright);
    } 
    int cross=maxleft+maxright;
    return max(cross,max(maxl,maxr));
    
}
int main(){
    int a[]={1,-4,1,3,-4,2};
    cout<<MaxSubArray(a,0,5)<<endl;
    return 0;
}