Time Limit: 3000MS | Memory Limit: 65536K | |
Total Submissions: 53647 | Accepted: 18522 |
Description
As an example, by inserting 2 characters, the string "Ab3bd" can be transformed into a palindrome ("dAb3bAd" or "Adb3bdA"). However, inserting fewer than 2 characters does not produce a palindrome.
Input
Output
Sample Input
5 Ab3bd
Sample Output
2
Source
问你增加多少字符使得字符串变成回文串
我们对字符串和他的逆序串求一个最长公共子序列,这样一来。LCS里的一定是回文的,而其它的一定不会回文,所以必须在对应位置插入那些字符使得他们对称,最后整个串才干够回文
#include <map> #include <set> #include <list> #include <stack> #include <queue> #include <vector> #include <cstdio> #include <cmath> #include <cstring> #include <iostream> #include <algorithm> using namespace std; char str1[5010]; char str2[5010]; int dp[2][5010]; int main() { int len; while (~scanf("%d", &len)) { scanf("%s", str1); for (int i = 0; i < len; i++) { str2[i] = str1[len - i - 1]; } str2[len] = '\0'; memset (dp, 0, sizeof(dp) ); for (int i = 1; i <= len; i++) { for (int j = 1; j <= len; j++) { if (str1[i - 1] == str2[j - 1]) { dp[i % 2][j] = dp[(i - 1) % 2][j - 1] + 1; } else { dp[i % 2][j] = max(dp[(i - 1) % 2][j], dp[i % 2][j - 1]); } } } printf("%d\n", len - dp[len % 2][len]); } }