日撸代码300行:第25天(二叉树深度遍历的栈实现 (中序))
2022/1/28 23:10:35
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代码来自闵老师”日撸 Java 三百行(21-30天)“,链接:https://blog.csdn.net/minfanphd/article/details/116975721
package datastructure.stack; /** * * Object stack. * * @author WX873 * */ public class ObjectStack { /** * The depth. */ public static final int MAX_DEPTH = 10; /** * The data. */ Object[] data; /** * The actual depth. */ int depth; /** * construct an empty char stack. */ public ObjectStack() { // TODO Auto-generated constructor stub depth = 0; data = new Object[MAX_DEPTH]; }//of the first constructor /** * *********************************************************** * Overrides the method claimed in Object, the superclass of any class. * *********************************************************** */ public String toString() { String resultString = ""; if (depth == 0) { System.out.println("The stack is empty!"); return null; }//of if for (int i = 0; i < depth; i++) { resultString += data[i] + ", "; }//of for i return resultString; }//of toString /** * ************************************************************** * Push an element. * * @param paraObject The given Object. * @return Push success or not. * ************************************************************** */ public boolean push(Object paraObject) { if (depth == MAX_DEPTH) { System.out.println("Stack full."); return false; }//of if data[depth] = paraObject; depth++; return true; }//of push /** * ************************************************************* * Pop an element. * * @return The Object at the top of the stack. * ************************************************************* */ public Object pop() { if (depth == 0) { System.out.println("No element to pop!"); return '\0'; }//of if depth--; return data[depth]; }//of pop /** * ************************************************************ * Is the stack empty? * * @return True, if empty. * ************************************************************ */ public boolean isEmpty() { if (depth == 0) { System.out.println("The stack is empty!"); return true; }//of if return false; }//of isEmpty /** * ************************************************************ * The entrance of the program. * * @param args Not used now. * ************************************************************ */ public static void main(String args[]) { ObjectStack tempStack = new ObjectStack(); for (char ch = 'a'; ch < 'm'; ch++) { tempStack.push(new Character(ch)); System.out.println("The current stack is: " + tempStack.toString()); }//of for ch char tempChar; for (int i = 0; i < 12; i++) { tempChar = ((Character)tempStack.pop()).charValue(); System.out.println("Poped: " + tempChar); System.out.println("The current stack is: " + tempStack.toString()); }//of for i }//of main }//of ObjectStack
这里自己写代码的时候,将pop()中的if语句里的返回值写成了“return null;”,结果运行的时候就报错。网上查了一下,‘\0’表示空字符。相当于这里还是有返回值,只是返回值为空字符。
return null;方法的返回值必须不是原始数据类型(封装类除外)和void。return 就是跳出方法;return null也是跳出方法并返回null。不要认为null就是没有值,null就是值。
原始类型 | 封装类
boolean | Boolean
char | Character
byte | Byte
short | Short
int | Integer
long | Long
float | Float
double | Double
关于原始类型与原始封装类的介绍:https://www.cnblogs.com/wisdo/p/4915774.html
/** * ****************************************************** * In-order visit with stack. * ****************************************************** */ public void inOrderVisitWithStack() { ObjectStack tempStack = new ObjectStack(); BinaryCharTree tempNode = this; while (!tempStack.isEmpty() || tempNode != null) { if (tempNode != null) { tempStack.push(tempNode); tempNode = tempNode.leftChild; } else { tempNode = (BinaryCharTree) tempStack.pop(); System.out.println("" + tempNode.value + ""); tempNode = tempNode.rightChild; } }//of while }//of inOrderVisitWithStack /** * ********************************************************* * The entrance of the program. * * @param args Not used now * ********************************************************* */ public static void main(String args[]) { BinaryCharTree tempTree = manualConstructTree(); System.out.println("\r\nPre-order visit:"); tempTree.preOrderVisit(); System.out.println("\r\nIn-order visit:"); tempTree.inOrderVisit(); System.out.println("\r\nPost-order visit:"); tempTree.postOrderVisit(); int tempDepth = tempTree.getDepth(); System.out.println("\nThe depth is: " + tempDepth); System.out.println("\rThe number of nodes for the binary tree is: " + tempTree.getNumNodes()); tempTree.toDataArrays(); System.out.println("The values are: " + Arrays.toString(tempTree.valueArray)); System.out.println("The indices are: " + Arrays.toString(tempTree.indicesArray)); tempTree.toDataArraysObjectQueue(); System.out.println("Only object queue."); System.out.println("The values are: " + Arrays.toString(tempTree.valueArray)); System.out.println("The indices are: " + Arrays.toString(tempTree.indicesArray)); tempTree.toDataArrayGenericQueue(); System.out.println("Generic queue."); System.out.println("The values are: " + Arrays.toString(tempTree.valueArray)); System.out.println("The indices are: " + Arrays.toString(tempTree.indicesArray)); //char[] tempCharArray = {'A','B','C','D','E','F'}; //int[] tempIndicesArray = {0, 1, 2, 4, 5, 12}; char[] tempCharArray = {'a','b','c','d','e','f','g'}; int[] tempIndicesArray = {0, 1, 2, 4, 5, 9, 10}; BinaryCharTree tempTree2 = new BinaryCharTree(tempCharArray, tempIndicesArray); System.out.println("\r\nPre-order visit:"); tempTree2.preOrderVisit(); System.out.println("\r\nIn-order visit:"); tempTree2.inOrderVisit(); System.out.println("\r\nPost-order visit:"); tempTree2.postOrderVisit(); System.out.println("\r\nIn-order visit with stack:"); tempTree2.inOrderVisitWithStack(); }//of main
inOrderVisitWithStack()的设计思路相当巧妙,用一个while循环同时实现了入栈和出栈;入栈后指向左孩子节点,出栈后指向右孩子节点。
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