二叉樹深度廣度遍歷

import java.util.ArrayDeque;

public class BinaryTree {

	static class TreeNode {
		int value;
		TreeNode left;
		TreeNode right;

		public TreeNode(int value) {
			this.value = value;
		}
	}

	TreeNode root;

	public BinaryTree(int[] array) {
		root = makeBinaryTreeByArray(array, 1);
	}

	/**
	 * 採用遞歸的方式創建一顆二叉樹 傳入的是二叉樹的數組表示法 構造後是二叉樹的二叉鏈表表示法
	 */
	public static TreeNode makeBinaryTreeByArray(int[] array, int index) {
		if (index < array.length) {
			int value = array[index];
			if (value != 0) {
				TreeNode t = new TreeNode(value);
				array[index] = 0;
				t.left = makeBinaryTreeByArray(array, index * 2);
				t.right = makeBinaryTreeByArray(array, index * 2 + 1);
				return t;
			}
		}
		return null;
	}

	/**
	 * 深度優先遍歷，相當於先根遍歷 採用非遞歸實現 需要輔助數據結構：棧
	 */
	public void depthOrderTraversal() {
		if (root == null) {
			System.out.println("empty tree");
			return;
		}
		ArrayDeque<TreeNode> stack = new ArrayDeque<TreeNode>();
		stack.push(root);
		while (stack.isEmpty() == false) {
			TreeNode node = stack.pop(); //堆棧彈出
			System.out.print(node.value + "    ");
			if (node.right != null) {
				stack.push(node.right); //壓入堆棧
			}
			if (node.left != null) {
				stack.push(node.left);
			}
		}
		System.out.print("\n");
	}

	/**
	 * 廣度優先遍歷 採用非遞歸實現 需要輔助數據結構：隊列
	 * 尾進頭出
	 */
	public void levelOrderTraversal() {
		if (root == null) {
			System.out.println("empty tree");
			return;
		}
		ArrayDeque<TreeNode> queue = new ArrayDeque<TreeNode>();
		queue.add(root);
		while (queue.isEmpty() == false) {
			TreeNode node = queue.remove(); //移除隊列頭
			System.out.print(node.value + "    ");
			if (node.left != null) {
				queue.add(node.left); //在末尾添加
			}
			if (node.right != null) {
				queue.add(node.right);
			}
		}
		System.out.print("\n");
	}

	/** 
     *                  13
     *                 /  \
     *               65    5
     *              /  \    \
     *             97  25   37
     *            /    /\   /
     *           22   4 28 32
     */
	public static void main(String[] args) {
		int[] arr = { 0, 13, 65, 5, 97, 25, 0, 37, 22, 0, 4, 28, 0, 0, 32, 0 };
		BinaryTree tree = new BinaryTree(arr);
		tree.depthOrderTraversal();
		tree.levelOrderTraversal();
	}
}

參考文章：

http://outofmemory.cn/code-snippet/4189/biinary-tree-java
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