《JAVA面试题》--用Java实现《剑指Offer》书中的面试题.zip

package pointer_to_offer; import java.util.LinkedList; import java.util.Queue; /** * Created by Administrator on 2016/7/30. */ public class TreeTraverse { public static void horizontallyTraverse(TreeNode node) { //横向遍历 Queue<TreeNode> queue = new LinkedList<TreeNode>(); queue.add(node); /** * 每次只出队一个，从而保证每次都是左结点先打印，并且把左结点的左右子结点入队，再打印右结点并且把右节点的左右子结点入队 * 从而队列中的元素都是每一层整齐地从左向右排列，接着排列下一层 */ while (!queue.isEmpty()) { TreeNode temp = queue.poll(); print(temp.getValue()); TreeNode left = temp.getLeft();//先把左子树结点入队 if (left != null) { queue.add(left); } TreeNode right = temp.getRight();//再把右子树结点入队 if (right != null) { queue.add(right); } } } public static void preorderTraverse(TreeNode node) { //纵向前序 循环算法 LinkedList<TreeNode> stack = new LinkedList<TreeNode>(); //先输出Stack的顶部元素，再使用Stack后进先出的原理，先放入右子结点再放左子结点 //到叶子结点的时候，没有新的结点入队，就先输出上一层的左结点再输出上一层的右结点，再继续放入上一层的右节点的右左子结点 if (node != null) { stack.push(node); while (!stack.isEmpty()) { node = stack.pop(); print(node.getValue()); if (node.getRight() != null) stack.push(node.getRight()); if (node.getLeft() != null) stack.push(node.getLeft()); } } } public static void preorderTraverse2(TreeNode node) { //纵向前序 递归算法 if (node == null) return; print(node.getValue()); preorderTraverse2(node.getLeft()); preorderTraverse2(node.getRight()); } public static void inorderTraverse(TreeNode node) {//纵向中序 循环算法 if (node == null) return; LinkedList<TreeNode> stack = new LinkedList<>(); while (true) { //循环地把右和中放入stack，直到再也没有左子结点 while (node != null) { if (node.getRight() != null) { stack.push(node.getRight()); } stack.push(node); node = node.getLeft();//对当前结点的左子结点进行操作 } node = stack.pop();//获取stack顶层结点——没有左子结点的一个结点 while (node.getRight() == null) { //如果这个结点也没有右子结点，那么直接输出 print(node.getValue()); if (stack.isEmpty()) return; node = stack.pop();//获取上一个结点——一定是现在结点的父结点 } //如果当前的结点有右子结点 //那么输出当前结点 //根据之前的逻辑，下一个stack出来的结点一定是当前结点的右结点 //将该右结点弹出，并且运用相同的逻辑遍历它的子孙结点们 print(node.getValue()); node = stack.pop(); } } public static void inorderTraverse2(TreeNode node) {//纵向中序 递归算法 if (node == null) return; inorderTraverse2(node.getLeft()); print(node.getValue()); inorderTraverse2(node.getRight()); } public static void postorderTraverse(TreeNode node) {//纵向后序 循环算法 TreeNode temp = node; LinkedList<TreeNode> stack = new LinkedList<TreeNode>(); while (node != null) { // 左子树入栈 for (; node.getLeft() != null; node = node.getLeft()) { stack.push(node); } //此时的node是一个没有左节点的节点，并且没有入栈 // 当前节点无右子——即只需要输出左和中;或右子刚刚已经输出，说明左右都已经输出，接着输出当前结点 while ((node.getRight() == null || node.getRight() == temp)) { print(node.getValue()); temp = node;// 记录上一个已输出节点 if (stack.isEmpty()) return; node = stack.pop(); } //当前结点下的左侧子结点已经处理完毕，接着处理右子结点 stack.push(node); node = node.getRight(); } } public static void postorderTraverse2(TreeNode node) {//纵向后序 递归算法 if (node == null) return; postorderTraverse2(node.getLeft()); postorderTraverse2(node.getRight()); print(node.getValue()); } private static void print(int val) { System.out.print(val + " "); } public static void main(String[] args) { TreeNode testTree = createNewTree(); // TODO System.out.println("\n-------horizontallyTraverse start-------- "); horizontallyTraverse(testTree); System.out.println("\n-------horizontallyTraverse finish-------- \n"); // 1 2 3 4 5 6 7 8 System.out.println("\n-------preorderTraverse loop start-------- "); preorderTraverse(testTree); System.out.println("\n-------preorderTraverse loop finish-------- \n"); System.out.println("\n-------preorderTraverse recursion start--------"); preorderTraverse2(testTree); System.out.println("\n-------preorderTraverse recursion finish-------- \n"); //1 2 4 8 5 3 6 7 System.out.println("\n-------inorderTraverse loop start-------- "); inorderTraverse(testTree); System.out.println("\n-------inorderTraverse loop finish-------- \n"); System.out.println("\n-------inorderTraverse recursion start-------- "); inorderTraverse2(testTree); System.out.println("\n-------inorderTraverse recursion finish-------- \n"); // 8 4 2 5 1 6 3 7 System.out.println("\n-------postorderTraverse loop start-------- "); postorderTraverse(testTree); System.out.println("\n-------postorderTraverse loop finish-------- \n"); System.out.println("\n-------postorderTraverse recursion start-------- "); postorderTraverse2(testTree); System.out.println("\n-------postorderTraverse recursion finish-------- \n"); //8 4 5 2 6 7 3 1 } /** * 1 * / \ * 2 3 * / \ / \ * 4 5 6 7 * / * 8 */ private static TreeNode createNewTree() { TreeNode root = new TreeNode(1); TreeNode node2 = new TreeNode(2); TreeNode node3 = new TreeNode(3); TreeNode node4 = new TreeNode(4); TreeNode node5 = new TreeNode(5); TreeNode node6 = new TreeNode(6); TreeNode node7 = new TreeNode(7); TreeNode node8 = new TreeNode(8); root.setLeft(node2); root.setRight(node3); node2.setLeft(node4); node2.setRight(node5); node3.setLeft(node6); node3.setRight(node7); node4.setLeft(node8); return root; } private static class TreeNode { private TreeNode left; private TreeNode right; private TreeNode parent; private final Integer value; TreeNode(Integer value) { this.value = value; } Integer getValue() { return value; } TreeNode getLeft() { return left; } void setLeft(TreeNode left) { this.left = left; if (left != null) left.parent = this; }