AtCoder - 4130 K-th Substring
Problem Statement
You are given a string s. Among the different substrings of s, print the K-th lexicographically smallest one.
A substring of s is a string obtained by taking out a non-empty contiguous part in s. For example, if s = ababc
, a
, bab
and ababc
are substrings of s, while ac
, z
and an empty string are not. Also, we say that substrings are different when they are different as strings.
Let X=x1x2…xn and Y=y1y2…ym be two distinct strings. X is lexicographically larger than Y if and only if Y is a prefix of X or xj>yj where j is the smallest integer such that xj≠yj.
Constraints
- 1 ≤ |s| ≤ 5000
- s consists of lowercase English letters.
- 1 ≤ K ≤ 5
- s has at least K different substrings.
Partial Score
- 200 points will be awarded as a partial score for passing the test set satisfying |s| ≤ 50.
Input
Input is given from Standard Input in the following format:
s
K
Output
Print the K-th lexicographically smallest substring of K.
Sample Input 1
aba
4
Sample Output 1
b
s has five substrings: a
, b
, ab
, ba
and aba
. Among them, we should print the fourth smallest one, b
. Note that we do not count a
twice.
Sample Input 2
atcoderandatcodeer
5
Sample Output 2
andat
Sample Input 3
z
1
Sample Output 3
z 一看这种题第一反应:裸上SAM啊!
但是一看数据范围:艹这是连SAM都不用的傻逼题了。
因为字典序第K小肯定不会超过K位,所以直接暴力+去重就可以做了QWQ
#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int maxn=5005;
string ch[maxn*6];
char s[maxn];
int n,k,cnt;
int main(){
scanf("%s%d",s,&k),n=strlen(s);
for(int i=0,T;i<n;i++){
ch[++cnt]=s[i];
T=min(k,n-i);
for(int j=1;j<T;j++,cnt++) ch[cnt+1]=ch[cnt]+s[i+j];
} sort(ch+1,ch+cnt+1);
unique(ch+1,ch+cnt+1);
cout<<ch[k]<<endl;
return 0;
}
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