import java.util.Stack;

public class Graph {

    class Vertex{    //顶点
        public char lebel;
        public boolean visited;
        public Vertex(char lab){
            lebel = lab;
            visited = false;
        }
    }

    private final int maxVertices = 20 ;  //最大顶点数
    private Vertex vertexList[];
    private int adjMatrix[][];
    private int vertexCount;
    private Stack theStack;

    public Graph(){
        vertexList = new Vertex[maxVertices];
        adjMatrix = new int[maxVertices][maxVertices];
        vertexCount = 0;
        for(int y = 0 ; y < maxVertices ; y++){
            for(int x = 0 ; x < maxVertices ; x ++){
                adjMatrix[x][y] = 0;
            }
        }
        theStack = new Stack();
    }

    public void addVertex(char lab){
        vertexList[vertexCount++]=new Vertex(lab);
    }

    public void addEdge(int start,int end){
        adjMatrix[start][end] = 1;
        adjMatrix[end][start] = 1;
    }

    public void displayVertex(int v){
        System.out.println(vertexList[v].lebel);
    }

    public void dfs(){
        vertexList[0].visited = true;
        displayVertex(0);
        theStack.push(0);
        while (!theStack.isEmpty()){
            int v = getAdjUnvisitedVertes((int)theStack.peek());
            if(v == -1){
                theStack.pop();
            }else {
                vertexList[v].visited = true;
                displayVertex(v);
                theStack.push(v);
            }
        }
        for(int j = 0 ; j < vertexCount; j++){
            vertexList[j].visited = false;
        }
    }

    public int getAdjUnvisitedVertes(int v){
        for(int j = 0 ; j < vertexCount ; j ++){
            if(adjMatrix[v][j] == 1 && vertexList[j].visited == false){
                return j;
            }
        }
        return -1;
    }

    public static void main(String[] args) {
        int col = 9 ;
        int[][] a = new int[col][col];
        a[0][1] = 1;a[0][5] = 1;a[1][2] = 1;a[1][6]= 1;a[1][8]= 1;
        a[2][3] = 1; a[2][8] = 1;
        a[3][8] =1; a[3][6]= 1; a[3][7] = 1;a[3][4] = 1;
        a[4][5] =1; a[4][7]= 1; a[5][6] = 1;a[6][7] = 1;

        Graph graph = new Graph();
        graph.addVertex('A');
        graph.addVertex('B');
        graph.addVertex('C');
        graph.addVertex('D');
        graph.addVertex('E');
        graph.addVertex('F');
        graph.addVertex('G');
        graph.addVertex('H');
        graph.addVertex('I');
        for(int y = 0 ; y < col; y ++){
            for(int x = 0 ; x < col ; x ++ ){
                if(a[y][x] == 1){
                   graph.addEdge(y,x);
                }
            }
        }
        graph.dfs();

    }

}