int s(int l,int r,int k)//二分查找
76 {
77 int mid;
78 while(l<=r)
79 {
80 mid=(l+r)>>1;
81 if(k<x[mid]) r=mid-1;
82 else if(k>x[mid]) l=mid+1;
83 else return mid;
84 }
85 return -1;
86 }