折半查找

Binary_Search(SeqList L,ElemType key,int n){
int low=0,high=n-1,mid;
while(low<=high){
mid=(low+high)/2;
if(L.elem[mid]==key)
return mid;
else if(L.elem[mid]>key)
high=mid-1;
else low=mid+1;
}
return -1;