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^...^

#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<string.h>
using namespace std;
bool judge[10];
int m,n;
bool check(int x){
memset(judge,false,sizeof(judge));
bool flag=true;
while(x){
int temp=x%10;
x/=10;
if(judge[temp]){
    flag=false;
    break;
}
judge[temp]=true;

}return flag;
}
int arr[100000000];
int main(){
    int tot=0;
for(int i=1;i<10000000;++i){
    if(check(i))arr[tot++]=i;
}

while(cin>>n){
    int r=tot-1;int l=0;
    int mid,res;
    if(n<=1){
        cout<<"0"<<endl;
        continue;
    }
    while(l<=r){
        mid=(l+r)/2;
        if(arr[mid]<n)
        {l=mid+1;
        res=mid;
        }
        else r=mid-1;
    }
    int s=res+1;
    cout<<s<<endl;
}
}