最长公共子序列(LCS)

POJ-Prob.1458 看算法导论3 自己用java写的,flag可以不用,课后题要求用min(m,n)+O(1)的空间完成...改天再写.

import java.util.Scanner;

/**
 * Created by IntelliJ IDEA.
 * User: mayday
 * Date: 13-2-15
 * Time: 下午5:03
 */
public class Main {
    public static int m, n;

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str1 = scanner.next();
        String str2 = scanner.next();
        m = str1.length();
        n = str2.length();
        Print_LCS(Length_Of_LCS(str1, str2), str1, m, n);
    }

    private static void Print_LCS(int[][] b, String str1, int i, int j) {
        if (i == 0 || j == 0)
            return;
        if (b[i][j] == 2) {
            Print_LCS(b, str1, i - 1, j - 1);
            System.out.print(str1.charAt(i - 1));
        } else if (b[i][j] == 1)
            Print_LCS(b, str1, i - 1, j);
        else
            Print_LCS(b, str1, i, j - 1);
    }

    private static int[][] Length_Of_LCS(String str1, String str2) {

        int c[][] = new int[m + 1][n + 1];
        int flag[][] = new int[m + 1][n + 1];
        for (int i = 0; i <= m; i++) {
            c[i][0] = 0;
            flag[i][0] = 0;
        }
        for (int j = 0; j <= n; ++j) {
            c[0][j] = 0;
            flag[0][j] = 0;
        }
        for (int i = 1; i <= m; i++)
            for (int j = 1; j <= n; j++) {
                if (str1.charAt(i - 1) == str2.charAt(j - 1)) {
                    c[i][j] = c[i - 1][j - 1] + 1;
                    flag[i][j] = 2;
                } else {
                    c[i][j] = Math.max(c[i - 1][j], c[i][j - 1]);
                    if (c[i - 1][j] >= c[i][j - 1]) {
                        flag[i][j] = 1;
                    }
                }
            }
        return flag;
    }
}