Title
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].
Note: The length of path between two nodes is represented by the number of edges between them.
Solution
这题目是求最长路径长度所覆盖的边，下面的是我做的，但是复杂了，重复计算
//cpp:
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int depth(TreeNode* t){
if(!t)
return 0;
return 1+max(depth(t->left),depth(t->right));
}
int diameterOfBinaryTree(TreeNode* root) {
if(!root)
return 0;
return max(depth(root->left)+depth(root->right)+1-1,max(diameterOfBinaryTree(root->left),diameterOfBinaryTree(root->right)));
}
};
改进
参考solution，发现，直接在depth中求Max(ans)就好了，因为在求root的maxdepth的时候会递归到所有的节点
class Solution {
int ans;
public int diameterOfBinaryTree(TreeNode root) {
ans = 1;
depth(root);
return ans - 1;
}
public int depth(TreeNode node) {
if (node == null) return 0;
int L = depth(node.left);
int R = depth(node.right);
ans = Math.max(ans, L+R+1);
return Math.max(L, R) + 1;
}
}