feat: add solutions to lc problem: No.0145

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution.cpp

@@ -13,26 +13,15 @@ class Solution {
 public:
     vector<int> postorderTraversal(TreeNode* root) {
         vector<int> ans;
-        while (root) {
-            if (!root->right) {
-                ans.push_back(root->val);
-                root = root->left;
-            } else {
-                TreeNode* next = root->right;
-                while (next->left && next->left != root) {
-                    next = next->left;
-                }
-                if (!next->left) {
-                    ans.push_back(root->val);
-                    next->left = root;
-                    root = root->right;
-                } else {
-                    next->left = nullptr;
-                    root = root->left;
-                }
+        function<void(TreeNode*)> dfs = [&](TreeNode* root) {
+            if (!root) {
+                return;
             }
-        }
-        reverse(ans.begin(), ans.end());
+            dfs(root->left);
+            dfs(root->right);
+            ans.push_back(root->val);
+        };
+        dfs(root);
         return ans;
     }
 };

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution.go

@@ -6,26 +6,16 @@
  *     Right *TreeNode
  * }
  */
-func postorderTraversal(root *TreeNode) []int {
-	var ans []int
-	for root != nil {
-		if root.Right == nil {
-			ans = append([]int{root.Val}, ans...)
-			root = root.Left
-		} else {
-			next := root.Right
-			for next.Left != nil && next.Left != root {
-				next = next.Left
-			}
-			if next.Left == nil {
-				ans = append([]int{root.Val}, ans...)
-				next.Left = root
-				root = root.Right
-			} else {
-				next.Left = nil
-				root = root.Left
-			}
+func postorderTraversal(root *TreeNode) (ans []int) {
+	var dfs func(*TreeNode)
+	dfs = func(root *TreeNode) {
+		if root == nil {
+			return
 		}
+		dfs(root.Left)
+		dfs(root.Right)
+		ans = append(ans, root.Val)
 	}
-	return ans
+	dfs(root)
+	return
 }

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution.java

@@ -14,10 +14,9 @@
  * }
  */
 class Solution {
-    private List<Integer> ans;
+    private List<Integer> ans = new ArrayList<>();
 
     public List<Integer> postorderTraversal(TreeNode root) {
-        ans = new ArrayList<>();
         dfs(root);
         return ans;
     }

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution.py

@@ -11,7 +11,6 @@ def dfs(root):
                 return
             dfs(root.left)
             dfs(root.right)
-            nonlocal ans
             ans.append(root.val)
 
         ans = []

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution.rs

@@ -19,19 +19,19 @@
 use std::rc::Rc;
 use std::cell::RefCell;
 impl Solution {
-    fn dfs(root: &Option<Rc<RefCell<TreeNode>>>, res: &mut Vec<i32>) {
+    fn dfs(root: &Option<Rc<RefCell<TreeNode>>>, ans: &mut Vec<i32>) {
         if root.is_none() {
             return;
         }
         let node = root.as_ref().unwrap().borrow();
-        Self::dfs(&node.left, res);
-        Self::dfs(&node.right, res);
-        res.push(node.val);
+        Self::dfs(&node.left, ans);
+        Self::dfs(&node.right, ans);
+        ans.push(node.val);
     }
 
     pub fn postorder_traversal(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<i32> {
-        let mut res = vec![];
-        Self::dfs(&root, &mut res);
-        res
+        let mut ans = vec![];
+        Self::dfs(&root, &mut ans);
+        ans
     }
 }

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution.ts

@@ -13,24 +13,15 @@
  */
 
 function postorderTraversal(root: TreeNode | null): number[] {
-    if (root == null) return [];
-    let stack = [];
-    let ans = [];
-    let prev = null;
-    while (root || stack.length) {
-        while (root) {
-            stack.push(root);
-            root = root.left;
+    const ans: number[] = [];
+    const dfs = (root: TreeNode | null) => {
+        if (!root) {
+            return;
         }
-        root = stack.pop();
-        if (!root.right || root.right == prev) {
-            ans.push(root.val);
-            prev = root;
-            root = null;
-        } else {
-            stack.push(root);
-            root = root.right;
-        }
-    }
+        dfs(root.left);
+        dfs(root.right);
+        ans.push(root.val);
+    };
+    dfs(root);
     return ans;
 }

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution2.cpp

@@ -0,0 +1,35 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    vector<int> postorderTraversal(TreeNode* root) {
+        vector<int> ans;
+        if (!root) {
+            return ans;
+        }
+        stack<TreeNode*> stk;
+        stk.push(root);
+        while (stk.size()) {
+            auto node = stk.top();
+            stk.pop();
+            ans.push_back(node->val);
+            if (node->left) {
+                stk.push(node->left);
+            }
+            if (node->right) {
+                stk.push(node->right);
+            }
+        }
+        reverse(ans.begin(), ans.end());
+        return ans;
+    }
+};

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution2.go

@@ -0,0 +1,29 @@
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func postorderTraversal(root *TreeNode) (ans []int) {
+	if root == nil {
+		return
+	}
+	stk := []*TreeNode{root}
+	for len(stk) > 0 {
+		node := stk[len(stk)-1]
+		stk = stk[:len(stk)-1]
+		ans = append(ans, node.Val)
+		if node.Left != nil {
+			stk = append(stk, node.Left)
+		}
+		if node.Right != nil {
+			stk = append(stk, node.Right)
+		}
+	}
+	for i, j := 0, len(ans)-1; i < j; i, j = i+1, j-1 {
+		ans[i], ans[j] = ans[j], ans[i]
+	}
+	return
+}

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution2.ts

@@ -13,9 +13,17 @@
  */
 
 function postorderTraversal(root: TreeNode | null): number[] {
-    if (root == null) {
-        return [];
+    const ans: number[] = [];
+    if (!root) {
+        return ans;
     }
-    const { val, left, right } = root;
-    return [...postorderTraversal(left), ...postorderTraversal(right), val];
+    const stk: TreeNode[] = [root];
+    while (stk.length) {
+        const { left, right, val } = stk.pop();
+        ans.push(val);
+        left && stk.push(left);
+        right && stk.push(right);
+    }
+    ans.reverse();
+    return ans;
 }

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution3.cpp

@@ -0,0 +1,38 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    vector<int> postorderTraversal(TreeNode* root) {
+        vector<int> ans;
+        while (root) {
+            if (!root->right) {
+                ans.push_back(root->val);
+                root = root->left;
+            } else {
+                TreeNode* next = root->right;
+                while (next->left && next->left != root) {
+                    next = next->left;
+                }
+                if (next->left != root) {
+                    ans.push_back(root->val);
+                    next->left = root;
+                    root = root->right;
+                } else {
+                    next->left = nullptr;
+                    root = root->left;
+                }
+            }
+        }
+        reverse(ans.begin(), ans.end());
+        return ans;
+    }
+};

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution3.go

@@ -0,0 +1,30 @@
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func postorderTraversal(root *TreeNode) (ans []int) {
+	for root != nil {
+		if root.Right == nil {
+			ans = append([]int{root.Val}, ans...)
+			root = root.Left
+		} else {
+			next := root.Right
+			for next.Left != nil && next.Left != root {
+				next = next.Left
+			}
+			if next.Left == nil {
+				ans = append([]int{root.Val}, ans...)
+				next.Left = root
+				root = root.Right
+			} else {
+				next.Left = nil
+				root = root.Left
+			}
+		}
+	}
+	return
+}

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution3.ts

@@ -13,19 +13,19 @@
  */
 
 function postorderTraversal(root: TreeNode | null): number[] {
-    const res = [];
-    while (root != null) {
+    const ans: number[] = [];
+    while (root !== null) {
         const { val, left, right } = root;
-        if (right == null) {
-            res.push(val);
+        if (right === null) {
+            ans.push(val);
             root = left;
         } else {
             let next = right;
-            while (next.left != null && next.left != root) {
+            while (next.left !== null && next.left !== root) {
                 next = next.left;
             }
-            if (next.left == null) {
-                res.push(val);
+            if (next.left === null) {
+                ans.push(val);
                 next.left = root;
                 root = right;
             } else {
@@ -34,5 +34,5 @@ function postorderTraversal(root: TreeNode | null): number[] {
             }
         }
     }
-    return res.reverse();
+    return ans.reverse();
 }