Codeforces Round #265 (Div. 2) C. No to Palindromes!

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Paul hates palindromes. He assumes that strings is tolerable if each its character is one of the firstp letters of the English alphabet and s doesn‘t contain any palindrome contiguous substring of length 2 or more.

Paul has found a tolerable string s of lengthn. Help him find the lexicographically next tolerable string of the same length or else state that such string does not exist.

Input

The first line contains two space-separated integers: n andp (1?≤?n?≤?1000;1?≤?p?≤?26). The second line contains strings, consisting of n small English letters. It is guaranteed that the string is tolerable (according to the above definition).

Output

If the lexicographically next tolerable string of the same length exists, print it. Otherwise, print "NO" (without the quotes).

Sample test(s)Input

3 3cba

Output

NO

Input

3 4cba

Output

cbd

Input

4 4abcd

Output

abda

Note

String s is lexicographically larger (or simply larger) than stringt with the same length, if there is numberi, such that s_{1?=?t1, ...,si?=?ti,si?+?1?>?ti?+?1.}

The lexicographically next tolerable string is the lexicographically minimum tolerable string which is larger than the given one.

A palindrome is a string that reads the same forward or reversed.

題意：求滿足大於給定串的序列，而且兩個序列都不包含長度大於等於2的迴文子串

思路：首先，因為不能有長度大於等於2的子串，所以當前位置是不能和它的前一個和前第二個一樣的。因為給定串也是不包含迴文子串的，所以為了能找個一個最小的滿足條件的字串，我們從右往前改，找到一個滿足不與前兩個一樣的位置的話，那麼從這個位置往右就是填寫不構成迴文的最小串了

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int maxn = 1010;int n, p;char str[maxn], tmp;int find(const int &x) {if (x == -1) return 0;for (int i = 1; ; i++) {if (str[x] + i >= tmp) break;if (x > 0 && str[x-1] == str[x] + i) continue;if (x > 0 && str[x-2] == str[x] + i) continue;str[x] += i;return 1;}if (!find(x-1)) return 0;str[x] = 'a';for (int i = 0; ; i++) {if (str[x] + i >= tmp) break;if (x > 0 && str[x-1] == str[x] + i) continue;if (x > 1 && str[x-2] == str[x] + i) continue;str[x] += i;return 1;}return 0;}int main() {scanf("%d%d", &n, &p);tmp = 'a' + p;scanf("%s", str);if (find(n-1))printf("%s\n", str);else printf("NO\n");return 0;}

Codeforces Round #265 (Div. 2) C. No to Palindromes!