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Commit 6fd076f

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feat: add solutions to lc problem: No.0145 (doocs#2335)
No.0145.Binary Tree Postorder Traversal
1 parent 8a95663 commit 6fd076f

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15 files changed

+653
-376
lines changed

15 files changed

+653
-376
lines changed

‎solution/0100-0199/0145.Binary Tree Postorder Traversal/README.md‎

Lines changed: 233 additions & 127 deletions
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‎solution/0100-0199/0145.Binary Tree Postorder Traversal/README_EN.md‎

Lines changed: 233 additions & 127 deletions
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‎solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution.cpp‎

Lines changed: 8 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -13,26 +13,15 @@ class Solution {
1313
public:
1414
vector<int> postorderTraversal(TreeNode* root) {
1515
vector<int> ans;
16-
while (root) {
17-
if (!root->right) {
18-
ans.push_back(root->val);
19-
root = root->left;
20-
} else {
21-
TreeNode* next = root->right;
22-
while (next->left && next->left != root) {
23-
next = next->left;
24-
}
25-
if (!next->left) {
26-
ans.push_back(root->val);
27-
next->left = root;
28-
root = root->right;
29-
} else {
30-
next->left = nullptr;
31-
root = root->left;
32-
}
16+
function<void(TreeNode*)> dfs = [&](TreeNode* root) {
17+
if (!root) {
18+
return;
3319
}
34-
}
35-
reverse(ans.begin(), ans.end());
20+
dfs(root->left);
21+
dfs(root->right);
22+
ans.push_back(root->val);
23+
};
24+
dfs(root);
3625
return ans;
3726
}
3827
};

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

Lines changed: 10 additions & 20 deletions
Original file line numberDiff line numberDiff line change
@@ -6,26 +6,16 @@
66
* Right *TreeNode
77
* }
88
*/
9-
func postorderTraversal(root *TreeNode) []int {
10-
var ans []int
11-
for root != nil {
12-
if root.Right == nil {
13-
ans = append([]int{root.Val}, ans...)
14-
root = root.Left
15-
} else {
16-
next := root.Right
17-
for next.Left != nil && next.Left != root {
18-
next = next.Left
19-
}
20-
if next.Left == nil {
21-
ans = append([]int{root.Val}, ans...)
22-
next.Left = root
23-
root = root.Right
24-
} else {
25-
next.Left = nil
26-
root = root.Left
27-
}
9+
func postorderTraversal(root *TreeNode) (ans []int) {
10+
var dfs func(*TreeNode)
11+
dfs = func(root *TreeNode) {
12+
if root == nil {
13+
return
2814
}
15+
dfs(root.Left)
16+
dfs(root.Right)
17+
ans = append(ans, root.Val)
2918
}
30-
return ans
19+
dfs(root)
20+
return
3121
}

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

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -14,10 +14,9 @@
1414
* }
1515
*/
1616
class Solution {
17-
private List<Integer> ans;
17+
private List<Integer> ans = newArrayList<>();
1818

1919
public List<Integer> postorderTraversal(TreeNode root) {
20-
ans = new ArrayList<>();
2120
dfs(root);
2221
return ans;
2322
}

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

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,6 @@ def dfs(root):
1111
return
1212
dfs(root.left)
1313
dfs(root.right)
14-
nonlocal ans
1514
ans.append(root.val)
1615

1716
ans = []

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

Lines changed: 7 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -19,19 +19,19 @@
1919
use std::rc::Rc;
2020
use std::cell::RefCell;
2121
impl Solution {
22-
fn dfs(root: &Option<Rc<RefCell<TreeNode>>>, res: &mut Vec<i32>) {
22+
fn dfs(root: &Option<Rc<RefCell<TreeNode>>>, ans: &mut Vec<i32>) {
2323
if root.is_none() {
2424
return;
2525
}
2626
let node = root.as_ref().unwrap().borrow();
27-
Self::dfs(&node.left, res);
28-
Self::dfs(&node.right, res);
29-
res.push(node.val);
27+
Self::dfs(&node.left, ans);
28+
Self::dfs(&node.right, ans);
29+
ans.push(node.val);
3030
}
3131

3232
pub fn postorder_traversal(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<i32> {
33-
let mut res = vec![];
34-
Self::dfs(&root, &mut res);
35-
res
33+
let mut ans = vec![];
34+
Self::dfs(&root, &mut ans);
35+
ans
3636
}
3737
}

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

Lines changed: 9 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -13,24 +13,15 @@
1313
*/
1414

1515
function postorderTraversal(root: TreeNode | null): number[] {
16-
if (root == null) return [];
17-
let stack = [];
18-
let ans = [];
19-
let prev = null;
20-
while (root || stack.length) {
21-
while (root) {
22-
stack.push(root);
23-
root = root.left;
16+
const ans: number[] = [];
17+
const dfs = (root: TreeNode | null) => {
18+
if (!root) {
19+
return;
2420
}
25-
root = stack.pop();
26-
if (!root.right || root.right == prev) {
27-
ans.push(root.val);
28-
prev = root;
29-
root = null;
30-
} else {
31-
stack.push(root);
32-
root = root.right;
33-
}
34-
}
21+
dfs(root.left);
22+
dfs(root.right);
23+
ans.push(root.val);
24+
};
25+
dfs(root);
3526
return ans;
3627
}
Lines changed: 35 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,35 @@
1+
/**
2+
* Definition for a binary tree node.
3+
* struct TreeNode {
4+
* int val;
5+
* TreeNode *left;
6+
* TreeNode *right;
7+
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
8+
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
9+
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
10+
* };
11+
*/
12+
class Solution {
13+
public:
14+
vector<int> postorderTraversal(TreeNode* root) {
15+
vector<int> ans;
16+
if (!root) {
17+
return ans;
18+
}
19+
stack<TreeNode*> stk;
20+
stk.push(root);
21+
while (stk.size()) {
22+
auto node = stk.top();
23+
stk.pop();
24+
ans.push_back(node->val);
25+
if (node->left) {
26+
stk.push(node->left);
27+
}
28+
if (node->right) {
29+
stk.push(node->right);
30+
}
31+
}
32+
reverse(ans.begin(), ans.end());
33+
return ans;
34+
}
35+
};
Lines changed: 29 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,29 @@
1+
/**
2+
* Definition for a binary tree node.
3+
* type TreeNode struct {
4+
* Val int
5+
* Left *TreeNode
6+
* Right *TreeNode
7+
* }
8+
*/
9+
func postorderTraversal(root *TreeNode) (ans []int) {
10+
if root == nil {
11+
return
12+
}
13+
stk := []*TreeNode{root}
14+
for len(stk) > 0 {
15+
node := stk[len(stk)-1]
16+
stk = stk[:len(stk)-1]
17+
ans = append(ans, node.Val)
18+
if node.Left != nil {
19+
stk = append(stk, node.Left)
20+
}
21+
if node.Right != nil {
22+
stk = append(stk, node.Right)
23+
}
24+
}
25+
for i, j := 0, len(ans)-1; i < j; i, j = i+1, j-1 {
26+
ans[i], ans[j] = ans[j], ans[i]
27+
}
28+
return
29+
}

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