1152: binary search

1152: Two point search

Title Description
Find an element in an ordered sequence x.
Input
First enter a positive integer n(n<=100000), Indicates that the sequence has n It's an integer , Then enter... In descending order n It's an integer ;
Then there is a positive integer m, Express m Search times ;
And finally m It's an integer , Express m An integer to find x.
Output
For every search , There's a line of output . If there is an element to look for in the sequence x, Output element x The sequence number in the sequence （ The serial number from 0 Start ）; If there is no element to look for in the sequence x, The output "Not found!".
The sample input Copy
5
1 3 5 7 9
11
-1
1
2
3
4
5
6
7
8
9
10
Sample output Copy
Not found!
0
Not found!
1
Not found!
2
Not found!
3
Not found!
4
Not found!
source / classification

#include<stdio.h>
#include<string.h>
#define N 100000
/*  Two point search  low<=high x>a[mid]  Find... On the right , namely low=mid+1 x<a[mid]  Find on the left , namely high=mid-1 x=a[mid]  You can return the query results  */
int a[N];
int efind(int a[],int n,int k)
{
    
    int low=0,high=n-1,mid;
    while(low<=high)
    {
    
        mid=(low+high)/2;
        if(a[mid]==k)     return mid;
        else if(a[mid]<k) low=mid+1;
        else high=mid-1;
    }
    return -1;
}

int main(){
    
    int n,m,r=0,x;
    scanf("%d",&n);
    for(int i=0;i<n;i++){
    
        scanf("%d",&a[i]);
    }
    scanf("%d",&m);

    while(m--){
    
        scanf("%d",&x);
        r=efind(a,n,x);
        if(r!=-1) printf("%d\n",r);
        else printf("Not found!\n");
    }
    return 0;
}