hdu 5676（dfs）

ztr loves lucky numbers

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)

Problem Description

ztr loves lucky numbers. Everybody knows that positive integers are lucky if their decimal representation doesn't contain digits other than 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Lucky number is super lucky if it's decimal representation contains equal amount of digits 4 and 7. For example, numbers 47, 7744, 474477 are super lucky and 4, 744, 467 are not.

One day ztr came across a positive integer n. Help him to find the least super lucky number which is not less than n.

 

Input

There are T(1≤n≤105) cases

For each cases:

The only line contains a positive integer n(1≤n≤1018). This number doesn't have leading zeroes.

 

Output

For each cases
Output the answer

 

Sample Input

2450047

 

Sample Output

474747
解题思路：其实是一道比较简单的题目，用dfs搜一发即可。自己的代码写的好搓，参考了别人的代码。
#include<cstdio>#include<cstring>using namespace std;char s[50];bool found;int four,seven,len;void write(int len){    for(int i = 0; i < len/2; i++) printf("4");    for(int i = 0; i < len/2; i++) printf("7");    printf("\n");}void dfs(long long ans, long long res, int lens){    if(lens == len && !found){        found = true;        printf("%I64d\n", ans);    }    if(found) return;    res = res * 10 + s[lens] - '0';    if(res <= ans * 10 + 4 && four < len / 2){        four++;        dfs(ans * 10 + 4, res, lens + 1);        four--;        res /= 10;    }    if(found) return;    if(res <= ans * 10 + 7 && seven < len / 2){        seven++;        dfs(ans * 10 + 7, res, lens + 1);        seven--;        res /= 10;    }}int main(){    int T;scanf("%d", &T);    while(T--){        scanf("%s", s);        len = strlen(s);        if(len & 1) write(len + 1);        else{            four = seven = 0;            found = false;            dfs(0, 0, 0);            if(!found) write(len + 2);        }    }    return 0;}