Commit 740dce9

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feat: add Binary Tree Postorder Traversal

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+79

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+79

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Lines changed: 29 additions & 3 deletions

Original file line number	Diff line number	Diff line change
`@@ -1,8 +1,6 @@`
`1`	`1`	`package com.hi.dhl.algorithms.leetcode._145.java;`
`2`	`2`
`3`		`-import java.util.LinkedList;`
`4`		`-import java.util.List;`
`5`		`-import java.util.Stack;`
	`3`	`+import java.util.*;`
`6`	`4`
`7`	`5`	`/**`
`8`	`6`	`* <pre>`
`@@ -66,4 +64,32 @@ public List<Integer> postorderTraversal(TreeNode root) {`
`66`	`64`	`}`
`67`	`65`	`return list;`
`68`	`66`	`}`
	`67`	`+`
	`68`	`+ public List<Integer> postorderTraversal2(TreeNode root) {`
	`69`	`+ List<Integer> data = new LinkedList<>();`
	`70`	`+ if (root == null) return data;`
	`71`	`+`
	`72`	`+ Deque<TreeNode> stack = new ArrayDeque<>();`
	`73`	`+ TreeNode pre = null;`
	`74`	`+ while (root != null \|\| !stack.isEmpty()) {`
	`75`	`+ while (true) {`
	`76`	`+ if (root != null) {`
	`77`	`+ stack.push(root);`
	`78`	`+ root = root.left;`
	`79`	`+ } else {`
	`80`	`+ root = stack.peek();`
	`81`	`+ if (root.right != null && root.right != pre) {`
	`82`	`+ root = root.right;`
	`83`	`+ } else {`
	`84`	`+ break;`
	`85`	`+ }`
	`86`	`+ }`
	`87`	`+ }`
	`88`	`+`
	`89`	`+ pre = stack.pop();`
	`90`	`+ data.add(pre.val);`
	`91`	`+ root = null;`
	`92`	`+ }`
	`93`	`+ return data;`
	`94`	`+ }`
`69`	`95`	`}`

Lines changed: 22 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -84,6 +84,28 @@ class Solution {`
`84`	`84`
`85`	`85`	`return output;`
`86`	`86`	`}`
	`87`	`+`
	`88`	`+ // 方法三`
	`89`	`+ public List<Integer> preorderTraversal(TreeNode root) {`
	`90`	`+ List<Integer> data = new LinkedList<>();`
	`91`	`+ if (root == null) return data;`
	`92`	`+ Deque<TreeNode> stack = new ArrayDeque<>();`
	`93`	`+ while (root != null \|\| !stack.isEmpty()) {`
	`94`	`+ if (root != null) {`
	`95`	`+ stack.push(root);`
	`96`	`+ }`
	`97`	`+`
	`98`	`+ if (!stack.isEmpty()) {`
	`99`	`+ TreeNode node = stack.pop();`
	`100`	`+ data.add(node.val);`
	`101`	`+ if (node.right != null) {`
	`102`	`+ stack.push(node.right);`
	`103`	`+ }`
	`104`	`+ root = node.left;`
	`105`	`+ }`
	`106`	`+ }`
	`107`	`+ return data;`
	`108`	`+ }`
`87`	`109`	`}`
`88`	`110`	```
`89`	`111`

Lines changed: 28 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -66,6 +66,34 @@ class Solution {`
`66`	`66`	`return list;`
`67`	`67`	`}`
`68`	`68`
	`69`	`+ // 方法二`
	`70`	`+ public List<Integer> postorderTraversal2(TreeNode root) {`
	`71`	`+ List<Integer> data = new LinkedList<>();`
	`72`	`+ if (root == null) return data;`
	`73`	`+`
	`74`	`+ Deque<TreeNode> stack = new ArrayDeque<>();`
	`75`	`+ TreeNode pre = null;`
	`76`	`+ while (root != null \|\| !stack.isEmpty()) {`
	`77`	`+ while (true) {`
	`78`	`+ if (root != null) {`
	`79`	`+ stack.push(root);`
	`80`	`+ root = root.left;`
	`81`	`+ } else {`
	`82`	`+ root = stack.peek();`
	`83`	`+ if (root.right != null && root.right != pre) {`
	`84`	`+ root = root.right;`
	`85`	`+ } else {`
	`86`	`+ break;`
	`87`	`+ }`
	`88`	`+ }`
	`89`	`+ }`
	`90`	`+`
	`91`	`+ pre = stack.pop();`
	`92`	`+ data.add(pre.val);`
	`93`	`+ root = null;`
	`94`	`+ }`
	`95`	`+ return data;`
	`96`	`+ }`
`69`	`97`	`}`
`70`	`98`	```
`71`	`99`

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