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[折半查找]:折半查找的迭代函数
(1)构造递归调用终止的边界条件
(2)实现递归调用,使得每次递归调用都能够向最终解逼近一步。
一种情况是查找成功(即list[middle] = searchnum),另一种情况是查找失败的情况,需要将其while语句替换成为等价的if语句,并在then语句中进行递归调用。
只需将新的left和right作为参数传递给下一次递归调用函数中即可。
#include<iostream>
using namespace std;
int COMPARE(int x,int y){
/*compare x,and y,return -1 for less than, 0 for equal,1 for greater */
if(x<y) return -1;
else if (x==y) return 0;
else return 1;
}
int binsearch(int list[],int searchnum,int left,int right){
/*search list[0] <=list[1] <= . . . <=list[n-1]for searchnum. Return its position if found. Otherwise
return -1 */
int middle;
if(left <= right) {
middle = (left+right) / 2;
switch (COMPARE(list[middle],searchnum)) {
case -1:return binsearch(list,searchnum, middle +1 ,right);
case 0:return middle+1;
case 1:return binsearch(list, searchnum,left,middle -1);
}
}
return -1;
}
int main(){
int a[100],n,m;
while(cin>>n){
for(int i=0;i<n;i++)
cin>>a[i];
cin>>m;
cout<<binsearch(a,m,0,n-1);
}
}