uva11151-最长回文串

题目链接 http://acm.hust.edu.cn/vjudge/problem/19462

解题思路

把字符串翻转，与原字符串求LCS。

注意空串处理。

代码

#include<stdio.h>
#include<string.h>
#define MAX_LEN 1005
#define LOCAL
char str[MAX_LEN], re[MAX_LEN];
int dp[MAX_LEN];
void reverStr()
{
    int n = strlen(str);
    for(int i=1; i<=n; i++) re[n-i] = str[i];
    re[0] = ‘0‘;
}
int main()
{
    #ifdef LOCAL
        freopen("data.txt", "r", stdin);
        freopen("ans.txt", "w", stdout);
    #endif
    int t;
    scanf("%d", &t);
    while(t--) {
        getchar(); char ch = getchar();
        while(ch == ‘ ‘) ch = getchar();
        if(ch == ‘\n‘) { printf("0\n"); ungetc(ch, stdin); continue; }
        else ungetc(ch, stdin);
        scanf("%s", &str[1]); str[0] = ‘0‘;
        reverStr();
        memset(dp, 0, sizeof(dp));
        int n = strlen(str) - 1;
        int x;
        for(int i=1; i<=n; i++) {
            x = dp[0];
            for(int j=1; j<=n; j++) {
                if(str[i] == re[j]) { int y = dp[j]; dp[j] = x + 1; x = y; }
                else { x = dp[j]; dp[j] = dp[j]>dp[j-1]?dp[j]:dp[j-1]; }
            }
        }
        printf("%d\n", dp[n]);
    }
    return 0;
}