programming-examples/java/Data_Structures/DfsNoRecursion.java

import java.util.*;
import java.util.stream.Stream;

public class DfsNoRecursion {

	public static void dfs(List<Integer>[] graph, int root) {
		int n = graph.length;
		int[] curEdge = new int[n];
		int[] stack = new int[n];
		stack[0] = root;
		for (int top = 0; top >= 0; ) {
			int u = stack[top];
			if (curEdge[u] == 0) {
				System.out.println(u);
			}
			if (curEdge[u] < graph[u].size()) {
				int v = graph[u].get(curEdge[u]++);
				if (curEdge[v] == 0) {
					stack[++top] = v;
				}
			} else {
				--top;
			}
		}
	}

	// Usage example
	public static void main(String[] args) {
		List<Integer>[] g = Stream.generate(ArrayList::new).limit(3).toArray(List[]::new);

		g[0].add(1);
		g[1].add(0);
		g[0].add(2);

		dfs(g, 0);
		System.out.println();
		dfs(g, 1);
		System.out.println();
		dfs(g, 2);
	}
}