题目大意
给出一个字符串,这个字符串是由两个相同的字符串连接之后再加一个字母的到的,求原串。
思路
枚举加的字母是哪一个,之后分情况讨论,根据hash值来判定是否符合题目要求。注意判重。
CODE
#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define MAX 2000010
#define BASE 23333
using namespace std;
int length, mid;
char s[MAX];
unsigned long long _hash[MAX];
unsigned long long power[MAX];
int cnt;
char ans[MAX], now[MAX];
unsigned long long h_ans, h_now;
inline unsigned long long GetHash(int l, int r)
{
return _hash[r] - _hash[l - 1] * power[r - l + 1];
}
inline bool Judge(int dismiss)
{
static unsigned long long front, tail;
if(dismiss < mid) {
front = GetHash(1, dismiss - 1) * power[mid - dismiss] + GetHash(dismiss + 1, mid);
tail = GetHash(mid + 1, length);
}
else if(dismiss == mid) {
front = GetHash(1, mid - 1);
tail = GetHash(mid + 1, length);
}
else {
front = GetHash(1, mid - 1);
tail = GetHash(mid, dismiss - 1) * power[length - dismiss] + GetHash(dismiss + 1, length);
}
if(front == tail) {
if(h_ans == front) return false;
h_ans = front;
int top = 0;
if(dismiss <= mid)
for(int i = mid + 1; i <= length; ++i)
ans[++top] = s[i];
else
for(int i = 1; i < mid; ++i)
ans[i] = s[i];
return true;
}
return false;
}
int main()
{
cin >> length;
if(!(length&1)) {
puts("NOT POSSIBLE");
return 0;
}
mid = (length >> 1) + 1;
scanf("%s", s + 1);
power[0] = 1;
for(int i = 1; i <= length; ++i)
power[i] = power[i - 1] * BASE;
for(int i = 1; i <= length; ++i)
_hash[i] = _hash[i - 1] * BASE + s[i];
for(int i = 1; i <= length; ++i) {
cnt += Judge(i);
if(cnt > 1) break;
}
if(!cnt)
puts("NOT POSSIBLE");
if(cnt == 1)
puts(ans + 1);
if(cnt > 1)
puts("NOT UNIQUE");
return 0;
}
时间: 2024-10-09 23:28:19