#每日话题20160928# 笔试面试高频题目：二叉树的打印

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package problems_2016_09_28; import java.util.Deque; import java.util.LinkedList; import java.util.Queue; public class Problem_09_PrintBinaryTreeByLevelAndZigZag { public static class Node { public int value; public Node left; public Node right; public Node(int data) { this.value = data; } } public static void printByLevel(Node head) { if (head == null) { return; } Queue<Node> queue = new LinkedList<Node>(); int level = 1; Node last = head; Node nLast = null; queue.offer(head); System.out.print("Level " + (level++) + " : "); while (!queue.isEmpty()) { head = queue.poll(); System.out.print(head.value + " "); if (head.left != null) { queue.offer(head.left); nLast = head.left; } if (head.right != null) { queue.offer(head.right); nLast = head.right; } if (head == last && !queue.isEmpty()) { System.out.print("\nLevel " + (level++) + " : "); last = nLast; } } System.out.println(); } public static void printByZigZag(Node head) { if (head == null) { return; } Deque<Node> dq = new LinkedList<Node>(); int level = 1; boolean lr = true; Node cur = head; Node last = head; Node nLast = null; dq.offerFirst(head); pringLevelAndOrientation(level++, lr); while (!dq.isEmpty()) { if (lr) { cur = dq.pollFirst(); if (cur.left != null) { nLast = nLast == null ? cur.left : nLast; dq.offerLast(cur.left); } if (cur.right != null) { nLast = nLast == null ? cur.right : nLast; dq.offerLast(cur.right); } } else { cur = dq.pollLast(); if (cur.right != null) { nLast = nLast == null ? cur.right : nLast; dq.offerFirst(cur.right); } if (cur.left != null) { nLast = nLast == null ? cur.left : nLast; dq.offerFirst(cur.left); } } System.out.print(cur.value + " "); if (cur == last && !dq.isEmpty()) { lr = !lr; last = nLast; nLast = null; System.out.println(); pringLevelAndOrientation(level++, lr); } } System.out.println(); } public static void pringLevelAndOrientation(int level, boolean lr) { System.out.print("Level " + level + " from "); System.out.print(lr ? "left to right: " : "right to left: "); } // for test -- print tree public static void printTree(Node head) { System.out.println("Binary Tree:"); printInOrder(head, 0, "H", 17); System.out.println(); } public static void printInOrder(Node head, int height, String to, int len) { if (head == null) { return; } printInOrder(head.right, height + 1, "v", len); String val = to + head.value + to; int lenM = val.length(); int lenL = (len - lenM) / 2; int lenR = len - lenM - lenL; val = getSpace(lenL) + val + getSpace(lenR); System.out.println(getSpace(height * len) + val); printInOrder(head.left, height + 1, "^", len); } public static String getSpace(int num) { String space = " "; StringBuffer buf = new StringBuffer(""); for (int i = 0; i < num; i++) { buf.append(space); } return buf.toString(); } public static void main(String[] args) { Node head = new Node(1); head.left = new Node(2); head.right = new Node(3); head.left.left = new Node(4); head.right.left = new Node(5); head.right.right = new Node(6); head.right.left.left = new Node(7); head.right.left.right = new Node(8); printTree(head); System.out.println("==============="); printByLevel(head); System.out.println("==============="); printByZigZag(head); } }