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• import java.util.LinkedList;
import java.util.Queue;

/**

Given a binary tree, find the leftmost value in the last row of the tree.

Example 1:
Input:

2
/ \
1   3

Output:
1

Example 2:
Input:

1
/ \
2   3
/   / \
4   5   6
/
7

Output:
7
Note: You may assume the tree (i.e., the given root node) is not NULL.

*/
public class Find_Bottom_Left_Tree_Value {

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int findBottomLeftValue(TreeNode root) {

// bfs
if (root == null) {
return -1;
}

q.offer(root);
int currentLevelCount = 1;
int nextLevelCount = 0;

int result = root.val;

boolean isLevelLeftMost = false;

while (!q.isEmpty()) {
TreeNode current = q.poll();
currentLevelCount--;

// check leftmost
if (isLevelLeftMost) {
result = current.val;
isLevelLeftMost = false;
}

if (current.left != null) {
q.offer(current.left);
nextLevelCount++;
}
if (current.right != null) {
q.offer(current.right);
nextLevelCount++;
}

if (currentLevelCount == 0) {
currentLevelCount = nextLevelCount;
nextLevelCount = 0;

// mark next node of queue is the possible result
isLevelLeftMost = true;
}
}

return result;
}
}
}

############

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode() {}
*     TreeNode(int val) { this.val = val; }
*     TreeNode(int val, TreeNode left, TreeNode right) {
*         this.val = val;
*         this.left = left;
*         this.right = right;
*     }
* }
*/
class Solution {
public int findBottomLeftValue(TreeNode root) {
Queue<TreeNode> q = new ArrayDeque<>();
q.offer(root);
int ans = 0;
while (!q.isEmpty()) {
ans = q.peek().val;
for (int i = q.size(); i > 0; --i) {
TreeNode node = q.poll();
if (node.left != null) {
q.offer(node.left);
}
if (node.right != null) {
q.offer(node.right);
}
}
}
return ans;
}
}

• // OJ: https://leetcode.com/problems/find-bottom-left-tree-value/
// Time: O(N)
// Space: O(N)
class Solution {
public:
int findBottomLeftValue(TreeNode* root) {
int ans = 0;
queue<TreeNode*> q;
q.push(root);
while (q.size()) {
int cnt = q.size();
ans = q.front()->val;
while (cnt--) {
root = q.front();
q.pop();
if (root->left) q.push(root->left);
if (root->right) q.push(root->right);
}
}
return ans;
}
};

• # Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def findBottomLeftValue(self, root: Optional[TreeNode]) -> int:
q = deque([root])
ans = 0
while q:
ans = q[0].val
for _ in range(len(q)):
node = q.popleft()
if node.left:
q.append(node.left)
if node.right:
q.append(node.right)
return ans

############

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def findBottomLeftValue(self, root):
"""
:type root: TreeNode
:rtype: int
"""

def dfs(root, h, w):
if not root:
return (float("inf"), float("inf"), None)
left = dfs(root.left, h - 1, w - 1)
right = dfs(root.right, h - 1, w + 1)
return min((h, w, root.val), left, right)

return dfs(root, 0, 0)[2]


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

• /**
* Definition for a binary tree node.
* class TreeNode {
*     val: number
*     left: TreeNode | null
*     right: TreeNode | null
*     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
*         this.val = (val===undefined ? 0 : val)
*         this.left = (left===undefined ? null : left)
*         this.right = (right===undefined ? null : right)
*     }
* }
*/

function findBottomLeftValue(root: TreeNode | null): number {
let ans = 0;
const q = [root];
while (q.length) {
ans = q[0].val;
for (let i = q.length; i; --i) {
const node = q.shift();
if (node.left) {
q.push(node.left);
}
if (node.right) {
q.push(node.right);
}
}
}
return ans;
}


• // Definition for a binary tree node.
// #[derive(Debug, PartialEq, Eq)]
// pub struct TreeNode {
//   pub val: i32,
//   pub left: Option<Rc<RefCell<TreeNode>>>,
//   pub right: Option<Rc<RefCell<TreeNode>>>,
// }
//
// impl TreeNode {
//   #[inline]
//   pub fn new(val: i32) -> Self {
//     TreeNode {
//       val,
//       left: None,
//       right: None
//     }
//   }
// }
use std::rc::Rc;
use std::cell::RefCell;
use std::collections::VecDeque;
impl Solution {
pub fn find_bottom_left_value(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
let mut queue = VecDeque::new();
queue.push_back(root);
let mut res = 0;
while !queue.is_empty() {
res = queue.front().unwrap().as_ref().unwrap().borrow_mut().val;
for _ in 0..queue.len() {
let node = queue.pop_front().unwrap();
let mut node = node.as_ref().unwrap().borrow_mut();
if node.left.is_some() {
queue.push_back(node.left.take());
}
if node.right.is_some() {
queue.push_back(node.right.take());
}
}
}
res
}
}


• /**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int findBottomLeftValue(TreeNode root) {
queue.offer(root);
int bottomLeftValue = 0;
while (!queue.isEmpty()) {
int size = queue.size();
bottomLeftValue = queue.peek().val;
for (int i = 0; i < size; i++) {
TreeNode node = queue.poll();
TreeNode left = node.left, right = node.right;
if (left != null)
queue.offer(left);
if (right != null)
queue.offer(right);
}
}
return bottomLeftValue;
}
}

############

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode() {}
*     TreeNode(int val) { this.val = val; }
*     TreeNode(int val, TreeNode left, TreeNode right) {
*         this.val = val;
*         this.left = left;
*         this.right = right;
*     }
* }
*/
class Solution {
public int findBottomLeftValue(TreeNode root) {
Queue<TreeNode> q = new ArrayDeque<>();
q.offer(root);
int ans = 0;
while (!q.isEmpty()) {
ans = q.peek().val;
for (int i = q.size(); i > 0; --i) {
TreeNode node = q.poll();
if (node.left != null) {
q.offer(node.left);
}
if (node.right != null) {
q.offer(node.right);
}
}
}
return ans;
}
}

• // OJ: https://leetcode.com/problems/find-bottom-left-tree-value/
// Time: O(N)
// Space: O(N)
class Solution {
public:
int findBottomLeftValue(TreeNode* root) {
int ans = 0;
queue<TreeNode*> q;
q.push(root);
while (q.size()) {
int cnt = q.size();
ans = q.front()->val;
while (cnt--) {
root = q.front();
q.pop();
if (root->left) q.push(root->left);
if (root->right) q.push(root->right);
}
}
return ans;
}
};

• # Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def findBottomLeftValue(self, root: Optional[TreeNode]) -> int:
q = deque([root])
ans = 0
while q:
ans = q[0].val
for _ in range(len(q)):
node = q.popleft()
if node.left:
q.append(node.left)
if node.right:
q.append(node.right)
return ans

############

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def findBottomLeftValue(self, root):
"""
:type root: TreeNode
:rtype: int
"""

def dfs(root, h, w):
if not root:
return (float("inf"), float("inf"), None)
left = dfs(root.left, h - 1, w - 1)
right = dfs(root.right, h - 1, w + 1)
return min((h, w, root.val), left, right)

return dfs(root, 0, 0)[2]


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

• /**
* Definition for a binary tree node.
* class TreeNode {
*     val: number
*     left: TreeNode | null
*     right: TreeNode | null
*     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
*         this.val = (val===undefined ? 0 : val)
*         this.left = (left===undefined ? null : left)
*         this.right = (right===undefined ? null : right)
*     }
* }
*/

function findBottomLeftValue(root: TreeNode | null): number {
let ans = 0;
const q = [root];
while (q.length) {
ans = q[0].val;
for (let i = q.length; i; --i) {
const node = q.shift();
if (node.left) {
q.push(node.left);
}
if (node.right) {
q.push(node.right);
}
}
}
return ans;
}


• // Definition for a binary tree node.
// #[derive(Debug, PartialEq, Eq)]
// pub struct TreeNode {
//   pub val: i32,
//   pub left: Option<Rc<RefCell<TreeNode>>>,
//   pub right: Option<Rc<RefCell<TreeNode>>>,
// }
//
// impl TreeNode {
//   #[inline]
//   pub fn new(val: i32) -> Self {
//     TreeNode {
//       val,
//       left: None,
//       right: None
//     }
//   }
// }
use std::rc::Rc;
use std::cell::RefCell;
use std::collections::VecDeque;
impl Solution {
pub fn find_bottom_left_value(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
let mut queue = VecDeque::new();
queue.push_back(root);
let mut res = 0;
while !queue.is_empty() {
res = queue.front().unwrap().as_ref().unwrap().borrow_mut().val;
for _ in 0..queue.len() {
let node = queue.pop_front().unwrap();
let mut node = node.as_ref().unwrap().borrow_mut();
if node.left.is_some() {
queue.push_back(node.left.take());
}
if node.right.is_some() {
queue.push_back(node.right.take());
}
}
}
res
}
}