int maxsubsum(const int a[],int left,int right)
{
    int maxleftsum,maxrightsum;
    int leftbordersum,rightbordersum;
    int maxleftbordersum,maxrightbordersum;
    int center,i;
    if(left==right)
        if(a[left]>0)
            return a[left];
        else return 0;
        center=(left+right)/2;
       maxleftsum=maxsubsum(a,left,center);
        maxrightsum=maxsubsum(a,center+1,right);这个递归弄不懂，求高手指点一二
        leftbordersum=0;
        rightbordersum=0;
        maxleftbordersum=0;
        maxrightbordersum=0;
        for(i=center;i>=left;i--){
            leftbordersum+=a[i];
            if(leftbordersum>maxleftbordersum)
            maxleftbordersum=leftbordersum;}
        for(i=center+1;i<=right;i++){
            rightbordersum+=a[i];
            if(rightbordersum>maxrightbordersum)
            maxrightbordersum=rightbordersum;}
        return max3(maxleftsum,maxrightsum,maxleftbordersum+maxrightbordersum);

}
int maxsubsequence2(const int a[],int n)
{
    return maxsubsum(a,0,n-1);
}