洛谷P1435 回文字串(dp)

#include<cstdio>
#include<algorithm>
#include<cstring>
#define LL long long
// #define int long long  
using namespace std;
const int MAXN = 2 * 1e6 + 10, INF = 1e9 + 7, mod = 998244353;
inline int read() {
    char c = getchar(); int x = 0, f = 1;
    while(c < '0' || c > '9') {if(c == '-') f = -1; c = getchar();}
    while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
    return x * f;
}
int f[1001][1001], N;//f[i][j]:前缀1-i，后缀j-n的最长公共子序列
char s[MAXN];
main() {
    scanf("%s", s + 1);
    N = strlen(s + 1);
    for(int i = 1; i <= N; i++) {
        for(int j = N; j >= i + 1; j--) {
            f[i][j] = max(f[i - 1][j], f[i][j + 1]);
            if(s[i] == s[j]) f[i][j] = max(f[i][j], f[i - 1][j + 1] + 1);
            //printf("%d %d %d\n", i, j, f[i][j]);
        }
    }
    int ans = INF;
    for(int i = 1; i <= N; i++)
        ans = min(ans, N - 1 - f[i - 1][i + 1] * 2);        

    for(int i = 2; i <= N - 1; i++) {
        ans = min(ans, N - 2 - (f[i - 1][i + 2] * 2) + (s[i] != s[i + 1]));
    }

    printf("%d", ans);
    return 0;
}
/*
abbbbba
--

abab

abbab

abcdba
*/