区间dp一直写的是递归版本的, 竟然超时了, 学了一下非递归的写法.
#include <iostream>
#include <sstream>
#include <algorithm>
#include <cstdio>
#include <math.h>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <string.h>
#include <bitset>
#define REP(i,a,n) for(int i=a;i<=n;++i)
#define PER(i,a,n) for(int i=n;i>=a;--i)
#define hr putchar(10)
#define pb push_back
#define lc (o<<1)
#define rc (lc|1)
#define mid ((l+r)>>1)
#define ls lc,l,mid
#define rs rc,mid+1,r
#define x first
#define y second
#define io std::ios::sync_with_stdio(false)
#define endl '
'
#define DB(a) ({REP(__i,1,n) cout<<a[__i]<<' ';hr;})
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int P = 1e9+7, P2 = 998244353, INF = 0x3f3f3f3f;
ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;}
ll qpow(ll a,ll n) {ll r=1%P;for (a%=P;n;a=a*a%P,n>>=1)if(n&1)r=r*a%P;return r;}
ll inv(ll x){return x<=1?1:inv(P%x)*(P-P/x)%P;}
inline int rd() {int x=0;char p=getchar();while(p<'0'||p>'9')p=getchar();while(p>='0'&&p<='9')x=x*10+p-'0',p=getchar();return x;}
//head
const int N = 55;
char a[N], b[N];
bool dp[N][N][N][N];
int main() {
int t;
scanf("%d", &t);
while (t--) {
scanf("%s%s", a+1, b+1);
int n = strlen(a+1), m = strlen(b+1), ret = 0;
REP(d1,0,n)REP(d2,0,m) {
for (int l1=1,r1=d1; r1<=n; ++l1,++r1) {
for (int l2=1,r2=d2; r2<=m; ++l2,++r2) {
bool &ans = dp[l1][r1][l2][r2] = 0;
if (d1+d2<=1) ans = 1;
else {
if (d1>1&&a[l1]==a[r1]) ans|=dp[l1+1][r1-1][l2][r2];
if (d2>1&&b[l2]==b[r2]) ans|=dp[l1][r1][l2+1][r2-1];
if (d1&&d2) {
if (a[l1]==b[r2]) ans|=dp[l1+1][r1][l2][r2-1];
if (b[l2]==a[r1]) ans|=dp[l1][r1-1][l2+1][r2];
}
}
if (ans) ret = max(ret, d1+d2);
}
}
}
printf("%d
", ret);
}
}