LeetCode543. Diameter of Binary Tree

Description

Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

Example:

Given a binary tree

1

/ \

2 3

/ \

4 5

Return

3

, which is the length of the path

[4,2,1,3]

or

[5,2,1,3]

.

my program

思路：

int depth(TreeNode* root)

求树的高度，

int depthDiff(TreeNode* root)

求root的左子树和右子树的高度和。递归求树的

diameter

class Solution {
public:
int depth(TreeNode* root)
{
if (root == NULL) return 0;
return max(depth(root->left),depth(root->right))+1;
}

int depthDiff(TreeNode* root)
{
if(root == NULL) return 0;
return depth(root->left)+depth(root->right);
}

int diameterOfBinaryTree(TreeNode* root) {
if(root == NULL) return 0;
return max(depthDiff(root),max(diameterOfBinaryTree(root->left),diameterOfBinaryTree(root->right)));
}
};

Submission Details

106 / 106 test cases passed.

Status: Accepted

Runtime: 19 ms

Your runtime beats 18.82 % of cpp submissions.

other methods

C++ Solution with DFS

class Solution {
public:
int maxdiadepth = 0;

int dfs(TreeNode* root){
if(root == NULL) return 0;

int leftdepth = dfs(root->left);
int rightdepth = dfs(root->right);

if(leftdepth + rightdepth > maxdiadepth) maxdiadepth = leftdepth + rightdepth;
return max(leftdepth +1, rightdepth + 1);
}

int diameterOfBinaryTree(TreeNode* root) {
dfs(root);

return maxdiadepth;
}
};

C++_Recursive_with brief explanation

class Solution {
public:
int diameterOfBinaryTree(TreeNode* root) {
if(root == nullptr) return 0;
int res = depth(root->left) + depth(root->right);
return max(res, max(diameterOfBinaryTree(root->left), diameterOfBinaryTree(root->right)));
}

int depth(TreeNode* root){
if(root == nullptr) return 0;
return 1 + max(depth(root->left), depth(root->right));
}
};