82 lines
1.9 KiB
Java
82 lines
1.9 KiB
Java
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import java.util.*;
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import java.util.stream.Stream;
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public class SCCTarjanNoRecursion {
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public static List<List<Integer>> scc(List<Integer>[] graph) {
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int n = graph.length;
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int[] stack = new int[n];
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int st = 0;
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int[] stack_cur = new int[n];
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int[] stack_pos = new int[n];
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int[] stack_prev = new int[n];
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int[] index = new int[n];
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Arrays.fill(index, -1);
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int[] lowlink = new int[n];
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int time = 0;
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List<List<Integer>> components = new ArrayList<>();
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for (int u = 0; u < n; u++) {
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if (index[u] == -1) {
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int top = 0;
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stack_cur[top] = u;
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stack_pos[top] = 0;
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stack_prev[top] = -1;
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while (top >= 0) {
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int cur = stack_cur[top];
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int pos = stack_pos[top];
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if (index[cur] == -1) {
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index[cur] = time;
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lowlink[cur] = time;
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++time;
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stack[st++] = cur;
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}
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if (pos < graph[cur].size()) {
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int v = graph[cur].get(pos);
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++stack_pos[top];
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if (index[v] == -1) {
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++top;
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stack_cur[top] = v;
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stack_pos[top] = 0;
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stack_prev[top] = cur;
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} else {
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lowlink[cur] = Math.min(lowlink[cur], lowlink[v]);
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}
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} else {
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int prev = stack_prev[top];
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if (prev != -1) {
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lowlink[prev] = Math.min(lowlink[prev], lowlink[cur]);
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}
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if (lowlink[cur] == index[cur]) {
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List<Integer> component = new ArrayList<>();
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while (true) {
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int v = stack[--st];
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lowlink[v] = Integer.MAX_VALUE;
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component.add(v);
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if (v == cur)
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break;
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}
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components.add(component);
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}
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--top;
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}
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}
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}
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}
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return components;
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}
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// Usage example
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public static void main(String[] args) {
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List<Integer>[] g = Stream.generate(ArrayList::new).limit(3).toArray(List[]::new);
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g[2].add(0);
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g[2].add(1);
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g[0].add(1);
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g[1].add(0);
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List<List<Integer>> res = scc(g);
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System.out.println(res);
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}
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}
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