回溯法---n-着色问题（3）

以三色问题为例：

对给定无向图着色，相邻点颜色不能相同，限用3种颜色

在框架基础上的实现：

import java. util.Vector ;

public class ThreeColor extends CombineProblem {

    int[][] graph;

    int start ;

    public ThreeColor (int[][] graph, int start) {

         super();

         this.graph = graph;

         this.start = start;

         this.flag = false ;

         this.n = graph. length;

         this.x = new Integer[n];

    }

    @Override

    public Vector <Comparable> makeItem(int k) {

        Vector <Comparable> vec = new Vector<Comparable>();

         for ( int i = 1 ; i <= 3 ; i++) {

            vec .add( i);

         }

         return vec;

    }

    @Override

    public boolean complete (int k) {

         return k >= n;

    }

    @Override

    public void printSolution (int k) {

         for ( int i = 0 ; i < x.length; i ++) {

            System .out. print(x [i] + " ");

         }

        System .out. println();

    }

    @Override

    public boolean isPartial (int k) {

         for ( int i = 0 ; i < k; i++) {

             if ( graph[k ][i] == 1 && x [k] == x[i ]) {

                 return false ;

             }

         }

         return true ;

    }

}

主函数：

public class Main {

    public static void main (String[] args) {

         int[][] graph = { { 0, 1 , 1 , 0 }, { 1, 0, 0, 1 }, { 1 , 0 , 0 , 1 },

                 { 0 , 1 , 1 , 0 } };

         Problem p = new ThreeColor(graph , 0 );

        

         p .explore(0);

         if (! p.flag) {

            System .out. println("no solution!" );

         }

    }

}

运行结果：

1 2 2 1

1 2 2 3

1 2 3 1

1 3 2 1

1 3 3 1

1 3 3 2

2 1 1 2

2 1 1 3

2 1 3 2

2 3 1 2

2 3 3 1

2 3 3 2

3 1 1 2

3 1 1 3

3 1 2 3

3 2 1 3

3 2 2 1

3 2 2 3 

来自为知笔记(Wiz)