codeforces 128 B. String 優先隊列

標籤：優先隊列

連結：http://codeforces.com/contest/128/problem/B

B. Stringtime limit per test2 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard output

One day in the IT lesson Anna and Maria learned about the lexicographic order.

String x is lexicographically less than string y, if either x is a prefix of y (and x?≠?y), or there exists such i (1?≤?i?≤?min(|x|,?|y|)), thatxi?<?yi, and for any j (1?≤?j?<?i) xj?=?yj. Here |a| denotes the length of the string a. The lexicographic comparison of strings is implemented by operator < in modern programming languages??.

The teacher gave Anna and Maria homework. She gave them a string of length n. They should write out all substrings of the given string, including the whole initial string, and the equal substrings (for example, one should write out the following substrings from the string "aab": "a", "a", "aa", "ab", "aab", "b"). The resulting strings should be sorted in the lexicographical order. The cunning teacher doesn‘t want to check all these strings. That‘s why she said to find only the k-th string from the list. Help Anna and Maria do the homework.

Input

The first line contains a non-empty string that only consists of small Latin letters ("a"-"z"), whose length does not exceed 105. The second line contains the only integer k (1?≤?k?≤?105).

Output

Print the string Anna and Maria need — the k-th (in the lexicographical order) substring of the given string. If the total number of substrings is less than k, print a string saying "No such line." (without the quotes).

Sample test(s)input

aa2

output

a

input

abc5

output

bc

input

abab7

output

b

Note

In the second sample before string "bc" follow strings "a", "ab", "abc", "b".

題意：字典序排序子串，找出子串中的第n大。

做法：因為最多讓你找第100000大，所以可以用優先隊列。先放入單個的。然後不斷取出最小的，然後添加一個 其後面的字母，然後再放回隊列。 隊列裡len個串，最多放n次，所以複雜度 log(len)*n。 

但是vs2010 的優先隊列好像很慢。 另外一題有次也用到優先隊列，vs2010跑好幾分鐘跑不出來的資料，CB可以秒跑。 所以這題不要交vs2010，不然會逾時。

#pragma comment(linker, "/STACK:102400000,102400000")#include <stdio.h>#include <stdlib.h>#include <string.h>#include <limits.h>#include <malloc.h>#include <ctype.h>#include <math.h>#include <string>#include <iostream>#include <algorithm>using namespace std;#include <stack>#include <queue>#include <vector>#include <deque>#include <set>#include <map>struct point{int id;string ss;bool operator <(const point &b) const{return ss>b.ss;}};char str[100010];int main(){int n;scanf("%s %d",str,&n);//n>>str>>n;priority_queue<point>q;int len=strlen(str);for(int i=0;str[i];i++){point tem;tem.ss="";tem.ss=str[i];tem.id=i;q.push(tem);}int id=0;point ans;while(!q.empty()){point tem=q.top();q.pop();id++;if(id==n){ ans=tem;break;}tem.id++;if(tem.id<len){tem.ss+=str[tem.id];q.push(tem);}}if(id!=n){puts("No such line.");}else{cout<<ans.ss<<endl;}return 0;}

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codeforces 128 B. String 優先隊列