图的API及其两种实现（邻接矩阵,邻接表 ）

图上的基本分方法可以抽象如下

package lee.graph;import java.io.FileNotFoundException;public interface Graph {public void initGraph(String path) throws FileNotFoundException;public int getWeight(int v , int w);public int getFirstNeighbor(int v);public int getNextNeighbor(int v, int w);public void setWeight(int v, int w , int power);public void printGraph();public int getNumVertex();public int getNumEdge();public int getOutDegree(int v);public int getInDegree(int v);}

常见的实现有 邻接矩阵法 和邻接表法。 注意图上的算法 和图本书的存储方式是无关的， 很多书都没有严格区分这一点。

图上的算法 比如 最小生成树 最短路径 遍历 拓扑排序等，仅依赖与API而不是图的具体实现。后续的文章会给出图上的常用算法。

邻接矩阵的实现：

package lee.graph;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.util.Scanner;public class MatrixGraph implements Graph{private int numVertex;private int numEdge;private int[][]  matrix;public MatrixGraph(int numOfV , int numOfE){this.numEdge = numOfE;this.numVertex = numOfV;matrix = new int[numOfE][numOfE];}@Overridepublic void initGraph(String path) throws FileNotFoundException {for(int i =0 ; i<numVertex;i++){for(int j=0;j<numVertex;j++){matrix[i][j] = 999;}} Scanner in = new Scanner(new FileInputStream(path));  while (in.hasNext()) {              int i = in.nextInt();              int j = in.nextInt();              int weight = in.nextInt();             setWeight(i,j,weight); }}@Overridepublic int getWeight(int v, int w) {return matrix[v][w];}@Overridepublic int getFirstNeighbor(int v) {for(int i=0; i<numVertex;i++){if(matrix[v][i]!=999 &&v!=i ){return i;}}return -1;}@Overridepublic int getNextNeighbor(int v, int w) {for(int i=w+1; i<numVertex;i++){if(matrix[v][i]!=999 && v!=i){return i;}}return -1;}@Overridepublic void setWeight(int v, int w, int power) { matrix[v][w] = power;}@Overridepublic void printGraph() {for(int i=0; i< numVertex; i++){for(int j=0; j<numVertex; j++){if(matrix[i][j] != 999 && i!=j){System.out.println(i + " " + j + " " + matrix[i][j]);}}}}@Overridepublic int getNumVertex() {return numVertex;}@Overridepublic int getNumEdge() {return numEdge;}@Overridepublic int getOutDegree(int v) {int count=0;for(int i=0; i<numVertex; i++){if(matrix[v][i] != 999 && v!=i){count++;}}return count;}@Overridepublic int getInDegree(int v) {int count=0;for(int i=0; i<numVertex; i++){if(matrix[i][v] != 999 && v!=i){count++;}}return count;}}

注：  节点不连接时，记其权值为999

图的邻接表实现：

package lee.graph;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.util.Scanner;public class LinkedGraph implements Graph{private int numVertex;private int numEdge;ArrNode [] arr;public LinkedGraph(int numV,int numE){this.numEdge = numE;this.numVertex = numV;arr = new ArrNode[numV];for(int i=0;i<arr.length;i++){arr[i] = new ArrNode();}}@Overridepublic void initGraph(String path) throws FileNotFoundException {Scanner in = new Scanner(new FileInputStream(path));while(in.hasNext()){int i = in.nextInt();int j = in.nextInt();int k = in.nextInt();if(arr[i].next==null){arr[i].next = new GNode(j,k);}else{GNode p = arr[i].next;while(p.next!=null){p=p.next;}p.next = new GNode(j,k);}}}@Overridepublic int getWeight(int v, int w) {GNode p = arr[v].next;while(p!=null && p.num!=w){p=p.next;}if(p==null){return 999;}else{return p.weight;}}@Overridepublic int getFirstNeighbor(int v) {GNode p = arr[v].next;if(p==null){return -1;}else{return p.num;}}@Overridepublic int getNextNeighbor(int v, int w) {GNode p = arr[v].next;while(p!=null && p.num!=w){p=p.next;}if(p.num == w && p.next !=null){return p.next.num;}return -1;}@Overridepublic void setWeight(int v, int w, int power) {GNode p = arr[v].next;while(p.next!=null && p.num!=w){p=p.next;}if(p.num==w){p.weight=power;;}else{p.next = new GNode(w,power);}}@Overridepublic void printGraph() {for(int i=0;i<numVertex;i++){GNode p = arr[i].next;while(p!=null){System.out.println(i+" "+p.num+" "+p.weight);p=p.next;}}}@Overridepublic int getNumVertex() {return numVertex;}@Overridepublic int getNumEdge() {return numEdge;}class GNode{int num;int weight;GNode next;GNode(int n,int w){this.num = n;this.weight = w;}}class ArrNode{GNode next;}@Overridepublic int getOutDegree(int v) {int count=0;GNode p = arr[v].next;while(p!=null){p=p.next;count++;}return count;}@Overridepublic int getInDegree(int v) {int count=0;for(int i =0; i < numVertex; i++){if(v!=i && getWeight(i,v)!=999){count++;}}return count;}}