Task: Topological sort




Go: package main

import (
    "fmt"
    "strings"
)

var data = `
LIBRARY          LIBRARY DEPENDENCIES
=======          ====================
des_system_lib   std synopsys std_cell_lib des_system_lib dw02 dw01 ramlib ieee
dw01             ieee dw01 dware gtech
dw02             ieee dw02 dware
dw03             std synopsys dware dw03 dw02 dw01 ieee gtech
dw04             dw04 ieee dw01 dware gtech
dw05             dw05 ieee dware
dw06             dw06 ieee dware
dw07             ieee dware
dware            ieee dware
gtech            ieee gtech
ramlib           std ieee
std_cell_lib     ieee std_cell_lib
synopsys         `

func main() {
    g, in, err := parseLibComp(data)
    if err != nil {
        fmt.Println(err)
        return
    }
    order, cyclic := topSortKahn(g, in)
    if cyclic != nil {
        fmt.Println("Cyclic:", cyclic)
        return
    }
    fmt.Println("Order:", order)
}

type graph map[string][]string
type inDegree map[string]int






func parseLibComp(data string) (g graph, in inDegree, err error) {
    
    lines := strings.Split(data, "\n")
    if len(lines) < 3 || !strings.HasPrefix(lines[2], "=") {
        return nil, nil, fmt.Errorf("data format")
    }
    
    lines = lines[3:]
    
    g = graph{}
    in = inDegree{}
    for _, line := range lines {
        libs := strings.Fields(line)
        if len(libs) == 0 {
            continue 
        }
        lib := libs[0]
        g[lib] = g[lib]
        for _, dep := range libs[1:] {
            in[dep] = in[dep]
            if dep == lib {
                continue 
            }
            successors := g[dep]
            for i := 0; ; i++ {
                if i == len(successors) {
                    g[dep] = append(successors, lib)
                    in[lib]++
                    break
                }
                if dep == successors[i] {
                    break 
                }
            }
        }
    }
    return g, in, nil
}








func topSortKahn(g graph, in inDegree) (order, cyclic []string) {
    var L, S []string
    
    
    rem := inDegree{}
    for n, d := range in {
        if d == 0 {
            
            S = append(S, n)
        } else {
            
            rem[n] = d
        }
    }
    for len(S) > 0 {
        last := len(S) - 1 
        n := S[last]
        S = S[:last]
        L = append(L, n) 
        for _, m := range g[n] {
            
            
            
            if rem[m] > 0 {
                rem[m]--         
                if rem[m] == 0 { 
                    S = append(S, m) 
                }
            }
        }
    }
    
    for c, in := range rem {
        if in > 0 {
            
            for _, nb := range g[c] {
                if rem[nb] > 0 {
                    cyclic = append(cyclic, c)
                    break
                }
            }
        }
    }
    if len(cyclic) > 0 {
        return nil, cyclic
    }
    return L, nil
}


Java: import java.util.*;

public class TopologicalSort {

    public static void main(String[] args) {
        String s = "std, ieee, des_system_lib, dw01, dw02, dw03, dw04, dw05,"
                + "dw06, dw07, dware, gtech, ramlib, std_cell_lib, synopsys";

        Graph g = new Graph(s, new int[][]{
            {2, 0}, {2, 14}, {2, 13}, {2, 4}, {2, 3}, {2, 12}, {2, 1},
            {3, 1}, {3, 10}, {3, 11},
            {4, 1}, {4, 10},
            {5, 0}, {5, 14}, {5, 10}, {5, 4}, {5, 3}, {5, 1}, {5, 11},
            {6, 1}, {6, 3}, {6, 10}, {6, 11},
            {7, 1}, {7, 10},
            {8, 1}, {8, 10},
            {9, 1}, {9, 10},
            {10, 1},
            {11, 1},
            {12, 0}, {12, 1},
            {13, 1}
        });

        System.out.println("Topologically sorted order: ");
        System.out.println(g.topoSort());
    }
}

class Graph {
    String[] vertices;
    boolean[][] adjacency;
    int numVertices;

    public Graph(String s, int[][] edges) {
        vertices = s.split(",");
        numVertices = vertices.length;
        adjacency = new boolean[numVertices][numVertices];

        for (int[] edge : edges)
            adjacency[edge[0]][edge[1]] = true;
    }

    List<String> topoSort() {
        List<String> result = new ArrayList<>();
        List<Integer> todo = new LinkedList<>();

        for (int i = 0; i < numVertices; i++)
            todo.add(i);

        try {
            outer:
            while (!todo.isEmpty()) {
                for (Integer r : todo) {
                    if (!hasDependency(r, todo)) {
                        todo.remove(r);
                        result.add(vertices[r]);
                         
                        continue outer;
                    }
                }
                throw new Exception("Graph has cycles");
            }
        } catch (Exception e) {
            System.out.println(e);
            return null;
        }
        return result;
    }

    boolean hasDependency(Integer r, List<Integer> todo) {
        for (Integer c : todo) {
            if (adjacency[r][c])
                return true;
        }
        return false;
    }
}