Tree
Depth-First Search
Binary Tree
Description
Given the root
of a binary tree, return the number of uni-value subtrees .
A uni-value subtree means all nodes of the subtree have the same value.
Example 1:
Input: root = [5,1,5,5,5,null,5]
Output: 4
Example 2:
Input: root = []
Output: 0
Example 3:
Input: root = [5,5,5,5,5,null,5]
Output: 6
Constraints:
The number of the node in the tree will be in the range [0, 1000]
.
-1000 <= Node.val <= 1000
Solutions
Solution 1
Python3 Java C++ Go TypeScript JavaScript
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25 # 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 countUnivalSubtrees ( self , root : Optional [ TreeNode ]) -> int :
def dfs ( root ):
if root is None :
return True
l , r = dfs ( root . left ), dfs ( root . right )
if not l or not r :
return False
a = root . val if root . left is None else root . left . val
b = root . val if root . right is None else root . right . val
if a == b == root . val :
nonlocal ans
ans += 1
return True
return False
ans = 0
dfs ( root )
return ans
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41 /**
* 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 {
private int ans ;
public int countUnivalSubtrees ( TreeNode root ) {
dfs ( root );
return ans ;
}
private boolean dfs ( TreeNode root ) {
if ( root == null ) {
return true ;
}
boolean l = dfs ( root . left );
boolean r = dfs ( root . right );
if ( ! l || ! r ) {
return false ;
}
int a = root . left == null ? root . val : root . left . val ;
int b = root . right == null ? root . val : root . right . val ;
if ( a == b && b == root . val ) {
++ ans ;
return true ;
}
return false ;
}
}
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36 /**
* 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 :
int countUnivalSubtrees ( TreeNode * root ) {
int ans = 0 ;
function < bool ( TreeNode * ) > dfs = [ & ]( TreeNode * root ) -> bool {
if ( ! root ) {
return true ;
}
bool l = dfs ( root -> left );
bool r = dfs ( root -> right );
if ( ! l || ! r ) {
return false ;
}
int a = root -> left ? root -> left -> val : root -> val ;
int b = root -> right ? root -> right -> val : root -> val ;
if ( a == b && b == root -> val ) {
++ ans ;
return true ;
}
return false ;
};
dfs ( root );
return ans ;
}
};
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30 /**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func countUnivalSubtrees ( root * TreeNode ) ( ans int ) {
var dfs func ( * TreeNode ) bool
dfs = func ( root * TreeNode ) bool {
if root == nil {
return true
}
l , r := dfs ( root . Left ), dfs ( root . Right )
if ! l || ! r {
return false
}
if root . Left != nil && root . Left . Val != root . Val {
return false
}
if root . Right != nil && root . Right . Val != root . Val {
return false
}
ans ++
return true
}
dfs ( root )
return
}
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37 /**
* 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 countUnivalSubtrees ( root : TreeNode | null ) : number {
let ans : number = 0 ;
const dfs = ( root : TreeNode | null ) : boolean => {
if ( root == null ) {
return true ;
}
const l : boolean = dfs ( root . left );
const r : boolean = dfs ( root . right );
if ( ! l || ! r ) {
return false ;
}
if ( root . left != null && root . left . val != root . val ) {
return false ;
}
if ( root . right != null && root . right . val != root . val ) {
return false ;
}
++ ans ;
return true ;
};
dfs ( root );
return ans ;
}
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35 /**
* Definition for a binary tree node.
* function TreeNode(val, left, right) {
* this.val = (val===undefined ? 0 : val)
* this.left = (left===undefined ? null : left)
* this.right = (right===undefined ? null : right)
* }
*/
/**
* @param {TreeNode} root
* @return {number}
*/
var countUnivalSubtrees = function ( root ) {
let ans = 0 ;
const dfs = root => {
if ( ! root ) {
return true ;
}
const l = dfs ( root . left );
const r = dfs ( root . right );
if ( ! l || ! r ) {
return false ;
}
if ( root . left && root . left . val !== root . val ) {
return false ;
}
if ( root . right && root . right . val !== root . val ) {
return false ;
}
++ ans ;
return true ;
};
dfs ( root );
return ans ;
};
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