uva 10118 - Free Candies

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import java.io.*;import java.math.BigInteger;import java.util.*;public class Main   {    public static int dfs(int a,int b,int c,int d, int dp[][][][], int marked[][][][],int size, int[] basket, int[][] table){        if(marked[a][b][c][d]==1){            return dp[a][b][c][d];        }        if(count_candy(basket)>=5) {            marked[a][b][c][d] = 1;            return 0;        }        if(a<size){            int candy = 0;            basket[table[a][0]]^=1;            if(basket[table[a][0]] ==0) candy = 1;            dp[a][b][c][d] = Math.max(dp[a][b][c][d],dfs(a+1,b,c,d,dp,marked,size,basket,table)+candy);            basket[table[a][0]]^=1;        }        if(b<size){            int candy = 0;            basket[table[b][1]]^=1;            if(basket[table[b][1]] ==0) candy = 1;            dp[a][b][c][d] = Math.max(dp[a][b][c][d],dfs(a,b+1,c,d,dp,marked,size,basket,table)+candy);            basket[table[b][1]]^=1;        }        if(c<size){            int candy = 0;            basket[table[c][2]]^=1;            if(basket[table[c][2]] ==0) candy = 1;            dp[a][b][c][d] = Math.max(dp[a][b][c][d],dfs(a,b,c+1,d,dp,marked,size,basket,table)+candy);            basket[table[c][2]]^=1;        }        if(d<size){            int candy = 0;            basket[table[d][3]]^=1;            if(basket[table[d][3]] ==0) candy = 1;            dp[a][b][c][d] = Math.max(dp[a][b][c][d],dfs(a,b,c,d+1,dp,marked,size,basket,table)+candy);            basket[table[d][3]]^=1;        }        marked[a][b][c][d] = 1;        return dp[a][b][c][d];    }    public static int count_candy(int[] basket){        int count = 0;        for(int i=0;i<25;i++){            count+=basket[i];        }        return count;    }    public static void main (String [] args) throws Exception {        Scanner scan = new Scanner(System.in);        while(true){            int n = scan.nextInt();            if(n==0) return;            int table[][] = new int[n+1][5];            for(int i=0;i<n;i++){                for(int j=0;j<4;j++){                    table[i][j] = scan.nextInt();                }            }            int dp[][][][] = new int[n+1][n+1][n+1][n+1];            int marked[][][][] = new int[n+1][n+1][n+1][n+1];            int basket[] = new int[25];            int result = dfs(0,0,0,0,dp,marked,n,basket,table);            System.out.println(result);        }    }}

其实不算难题啦。。

和以前写的二维dfs走迷宫其实差不多的，无非是判重，深搜

没写过4维的，反映不过来，一些细节比如如何存candy和pair没想清楚。。。

写出来再看，其实还是很清晰的思路。四路都往下搜，中间判重就好。