最长公共子序列 LCS

int n,m;

char a[MAXN],b[MAXN],res[MAXN];

int dp[MAXN][MAXN],dir[MAXN][MAXN];
//dir 1斜上，2左，3上

void lcs(int al,int bl)
{
    int i,j;
    for(i=1;i<=al;i++)
    {
        for(j=1;j<=bl;j++)
        {
            if(a[i-1] == b[j-1])
            {
                dp[i][j] = dp[i-1][j-1]+1;
                dir[i][j] = 1;
            }
            else if(dp[i-1][j]>dp[i][j-1])
            {
                dp[i][j] = dp[i-1][j];
                dir[i][j] = 3;
            }
            else
            {
                dp[i][j] = dp[i][j-1];
                dir[i][j] = 2;
            }
        }
    }
}

void getlcs(int al,int bl)
{
    int i = al;
    int j = bl;
    int k = 0;
    while(i && j)
    {
        if(dir[i][j] == 1)
        {
            res[k++] = a[i-1];
            i--;j--;
        }
        else if(dir[i][j]==2) j--;
        else if(dir[i][j]==3) i--;
    }
    for(int v = k-1;v>=0;v--) pf("%c",res[v]);
}