每天刷个算法题20160518：非递归二叉树遍历
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http://blog.csdn.net/xiaofei_it/article/details/51502254
为了防止思维僵化，每天刷个算法题。已经刷了几天了，现在贴点代码。
2002年我初中二年级，开始学习BASIC语言。2004年中考之后，开始参加NOIP，系统学习算法。一直非常喜欢算法，但工作后几乎不再碰这些东西。现在准备重新捡起来。
我已经建了一个开源项目，每天的题目都在里面：
https://github.com/Xiaofei-it/Algorithms
绝大部分算法都是我自己写的，没有参考网上通用代码。读者可能会觉得有的代码晦涩难懂，因为那是我自己的理解。
最近几天都是在写一些原来的东西，大多数是非递归。以后准备刷点DP、贪心之类的题。
这里贴一个递归与非递归二叉树遍历。
前序遍历
/**
*
* Copyright 2016 Xiaofei
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package xiaofei.algorithm;
/**
* Created by Xiaofei on 16/5/18.
*/
public class PreOrderTraversal {
public static void traversalRecursively(BinaryTreeNode root) {
if (root == null) {
return;
}
System.out.print(root.data + " ");
traversalRecursively(root.left);
traversalRecursively(root.right);
}
public static void traversalCorecursively(BinaryTreeNode root) {
class StackElement {
BinaryTreeNode node;
boolean leftVisited;
boolean rightVisited;
}
StackElement[] stack = new StackElement[100];
for (int i = 0; i < 100; ++i) {
stack[i] = new StackElement();
}
int top = -1;
stack[++top] = new StackElement();
stack[top].node = root;
while (top >= 0) {
BinaryTreeNode node = stack[top].node;
if (!stack[top].leftVisited) {
System.out.print(node.data + " ");
stack[top].leftVisited = true;
if (node.left != null) {
stack[++top] = new StackElement();
stack[top].node = node.left;
}
} else if (!stack[top].rightVisited) {
stack[top].rightVisited = true;
if (node.right != null) {
stack[++top] = new StackElement();
stack[top].node = node.right;
}
} else {
--top;
}
}
}
}
中序遍历
/**
*
* Copyright 2016 Xiaofei
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package xiaofei.algorithm;
/**
* Created by Xiaofei on 16/5/18.
*/
public class InOrderTraversal {
public static void traversalRecursively(BinaryTreeNode root) {
if (root == null) {
return;
}
traversalRecursively(root.left);
System.out.print(root.data + " ");
traversalRecursively(root.right);
}
public static void traversalCorecursively(BinaryTreeNode root) {
class StackElement {
BinaryTreeNode node;
boolean leftVisited;
boolean rightVisited;
}
StackElement[] stack = new StackElement[100];
for (int i = 0; i < 100; ++i) {
stack[i] = new StackElement();
}
int top = -1;
stack[++top] = new StackElement();
stack[top].node = root;
while (top >= 0) {
BinaryTreeNode node = stack[top].node;
if (!stack[top].leftVisited) {
stack[top].leftVisited = true;
if (node.left != null) {
stack[++top] = new StackElement();
stack[top].node = node.left;
}
} else if (!stack[top].rightVisited) {
System.out.print(node.data + " ");
stack[top].rightVisited = true;
if (node.right != null) {
stack[++top] = new StackElement();
stack[top].node = node.right;
}
} else {
--top;
}
}
}
}
后序遍历
/**
*
* Copyright 2016 Xiaofei
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package xiaofei.algorithm;
/**
* Created by Xiaofei on 16/5/18.
*/
public class PostOrderTraversal {
public static void traversalRecursively(BinaryTreeNode root) {
if (root == null) {
return;
}
traversalRecursively(root.left);
traversalRecursively(root.right);
System.out.print(root.data + " ");
}
public static void traversalCorecursively(BinaryTreeNode root) {
class StackElement {
BinaryTreeNode node;
boolean leftVisited;
boolean rightVisited;
}
StackElement[] stack = new StackElement[100];
for (int i = 0; i < 100; ++i) {
stack[i] = new StackElement();
}
int top = -1;
stack[++top] = new StackElement();
stack[top].node = root;
while (top >= 0) {
BinaryTreeNode node = stack[top].node;
if (!stack[top].leftVisited) {
stack[top].leftVisited = true;
if (node.left != null) {
stack[++top] = new StackElement();
stack[top].node = node.left;
}
} else if (!stack[top].rightVisited) {
stack[top].rightVisited = true;
if (node.right != null) {
stack[++top] = new StackElement();
stack[top].node = node.right;
}
} else {
System.out.print(node.data + " ");
--top;
}
}
}
}