題意：正則表達式匹配

思路:DP dp[i][j]表示b串中0~i與0~j是否可以匹配，具體的轉移看代碼：

#include<cstdio>
#include<cstring>
#include<string>
using namespace std;
const int maxn=2600;
char a[maxn],b[maxn];
bool dp[maxn][maxn];

int main()
{
    freopen("input.txt","r",stdin);
    int T;scanf("%d",&T);
    while(T--)
    {
        scanf(
 
"%s%s",a+1,b+1);
        memset(dp,0,sizeof dp);
        dp[0][0]=1;
        int sa=strlen(a+1),sb=strlen(b+1);
        for(int i=1;i<=sb;i++)
        {
            if(b[i]==‘*‘&&i>=2)dp[i][0]=dp[i-2][0];
            for(int j=1;j<=sa;j++)
            {
                if(b[i]==a[j] || b[i]==‘
 
.‘)dp[i][j] = dp[i-1][j-1];
                else if(b[i]==‘*‘)
                {
                    dp[i][j] = dp[i-1][j] | dp[i-2][j];
                    dp[i][j] |= dp[i-1][j-1]&&(a[j]==a[j-1]);
                    if(dp[i-1][j])
                    {
                        while(j<=sa&&a[j]==a[j+1
 
])dp[i][++j]=1;
                    }
                }
            }
        }
        if(dp[sb][sa])
            printf("yes\n");
        else
            printf("no\n");
    }
    return 0;
}

hdu 6170