/* JLS $14.15. Test of break statement with labels.

In the following example, a mathematical graph is represented by an array of

arrays. A graph consists of a set of nodes and a set of edges; each edge is an arrow

that points from some node to some other node, or from a node to itself. In this

example it is assumed that there are no redundant edges; that is, for any two nodes

P and Q , where Q may be the same as P, there is at most one edge from P to Q .

Nodes are represented by integers, and there is an edge from node i to node

edges[ i ][ j ] for every i and j for which the array reference edges[ i ][ j ]

does not throw an IndexOutOfBoundsException.

The task of the method loseEdges, given integers i and j , is to construct a

new graph by copying a given graph but omitting the edge from node i to node j ,

if any, and the edge from node j to node i , if any.

Note the use of two statement labels, edgelist and search , and the use of break

statements. This allows the code that co pies a list, omitting on e edge, to be shared

between two separate tests, th e test for an edge from node i to node j , and the test

for an edge from node j to node i .

*/

class Graph {

int edges[][];

Graph(int[][] edges) {

this.edges = edges;

}

Graph loseEdges(int i, int j) {

int n = edges.length;

int[][] newedges = new int[n][];

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

edgelist:

{

int z;

search:

{

if (k == i) {

for (z = 0; z < edges[k].length; ++z)

if (edges[k][z] == j)

break search;

} else if (k == j) {

for (z = 0; z < edges[k].length; ++z)

if (edges[k][z] == i)

break search;

}

// No edge to be deleted; share this list.

newedges[k] = edges[k];

break edgelist;

} //search

// Copy the list, omitting the edge at position z.

int m = edges[k].length - 1;

int ne[] = new int[m];

arraycopy(edges[k], 0, ne, 0, z);

arraycopy(edges[k], z + 1, ne, z, m - z);

newedges[k] = ne;

} //edgelist

}

return new Graph(newedges);

}

void arraycopy(int[] src, int srcPos, int[] dest, int destPos,

int length) {

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

dest[destPos + i] = src[srcPos + i];

}

}

void print() {

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

System.out.print(i + " |-> ");

for (int j = 0; j < edges[i].length; j++) {

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

}

System.out.println();

}

}

}

public class graph_break {

public static void main(String[] args) {

int n = 4;

int[][] edges = new int[n][n];

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

for (int j = 0; j < n; j++) {

edges[i][j] = (i + j) % n;

}

}

Graph graph1 = new Graph(edges);

System.out.println("Init graph:");

graph1.print();

Graph graph2 = graph1.loseEdges(1,2);

System.out.println();

System.out.println("Graph without edges (1,2),(2,1):");

graph2.print();

System.out.println("Done!");

}

}

/*

Init graph:

0 |-> 0 1 2 3

1 |-> 1 2 3 0

2 |-> 2 3 0 1

3 |-> 3 0 1 2

Graph without edges (1,2),(2,1):

0 |-> 0 1 2 3

1 |-> 1 3 0

2 |-> 2 3 0

3 |-> 3 0 1 2

Done!

*/