二分法查找

 1 #include<stdio.h>
 2 int a[3000];
 3 int chazhao(int n,int t)
 4 {
 5     int x,y,m;
 6     x=0;y=n-1;
 7     if(a[x]==t)x=x;
 8     else if(a[y]==t) x=y;
 9     else while(x<y)
10     {
11         m=x+(y-x)/2;
12         if(a[m]>=t)y=m;
13         else x=m+1;
14     }
15     return x;
16 }
17 int main()
18 {
19     int n,i,t;
20     scanf("%d",&n);
21     for(i=0;i<n;i++)
22         scanf("%d",&a[i]);//输入一个有序数列
23     scanf("%d",&t);
24     i=chazhao(n,t);
25     if(a[i]==t) printf("%d\n",i+1);
26     else printf("No\n");
27     return 0;
28 }