枚举，二分

二分模板

① 普通的整数二分
int l, r, res;
while(l <= r){
int mid = (l + r) / 2;
if (ok (mid)){
res = mid;
r = mid - 1; 
}
else{
l = mid + 1; // 满足条件的最小值
}
}

精度精确型二分
const double eps = 1e-7;
double l， r;
while (l + eps < r){
double mid = (l + r) / 2.0;
if (ok (mid)){
l = mid;
}
else {
r = mid;
}
}

HDU4151 http://acm.hdu.edu.cn/showproblem.php?pid=4151

先是枚举，然后是二分^...^

 1 #include<stdio.h>
 2 #include<iostream>
 3 #include<algorithm>
 4 #include<string.h>
 5 using namespace std;
 6 bool judge[10];
 7 int m,n;
 8 bool check(int x){
 9 memset(judge,false,sizeof(judge));
10 bool flag=true;
11 while(x){
12 int temp=x%10;
13 x/=10;
14 if(judge[temp]){
15     flag=false;
16     break;
17 }
18 judge[temp]=true;
19
20 }return flag;
21 }
22 int arr[100000000];
23 int main(){
24     int tot=0;
25 for(int i=1;i<10000000;++i){
26     if(check(i))arr[tot++]=i;
27 }
28
29 while(cin>>n){
30     int r=tot-1;int l=0;
31     int mid,res;
32     if(n<=1){
33         cout<<"0"<<endl;
34         continue;
35     }
36     while(l<=r){
37         mid=(l+r)/2;
38         if(arr[mid]<n)
39         {l=mid+1;
40         res=mid;
41         }
42         else r=mid-1;
43     }
44     int s=res+1;
45     cout<<s<<endl;
46 }
47 }