【POJ】1692 Crossed Matchings

经典DP，想了很久，开始想复杂了。

#include <iostream>
using namespace std;

#define MAXNUM 100

int mymax(int a, int b) {
    return (a>b) ? a:b;
}

int main() {
    int case_n;
    int a_n, b_n;
    int i, j;
    int a[MAXNUM], b[MAXNUM];
    int match[MAXNUM][MAXNUM];
    int max_a2b[MAXNUM][MAXNUM], max_b2a[MAXNUM][MAXNUM];

    cin >>case_n;

    while (case_n--) {
        cin >>a_n>>b_n;
        for (i=1; i<=a_n; ++i)
            cin >>a[i];
        for (i=1; i<=b_n; ++i)
            cin >>b[i];
        for (i=0; i<=a_n; ++i) {
            match[i][0] = 0;
            max_a2b[i][0] = 0;
        }
        for (i=0; i<=b_n; ++i) {
            match[0][i] = 0;
            max_b2a[i][0] = 0;
        }
        for (i=1; i<=a_n; ++i)
            for (j=1; j<=b_n; ++j) {
                if (a[i] == b[j-1])
                    max_a2b[i][j] = j-1;
                else
                    max_a2b[i][j] = max_a2b[i][j-1];
            }
        for (i=1; i<=b_n; ++i)
            for (j=1; j<=a_n; ++j) {
                if (b[i] == a[j-1])
                    max_b2a[i][j] = j-1;
                else
                    max_b2a[i][j] = max_b2a[i][j-1];
            }

        int pos_b, pos_a;
        for (i=1; i<=a_n; ++i) {
            for (j=1; j<=b_n; ++j) {
                match[i][j] = mymax(match[i-1][j], match[i][j-1]);
                pos_b = max_a2b[i][j];
                pos_a = max_b2a[j][i];
                if (pos_b>0 && pos_a>0 && a[i] != b[j]) {
                    match[i][j] = mymax(match[i][j], match[pos_a-1][pos_b-1]+2);
                }
            }
        }

        cout <<match[a_n][b_n]<<endl;
    }

    return 0;
}