Diameter of Binary Tree

最新推荐文章于 2024-09-23 05:15:06 发布

原创最新推荐文章于 2024-09-23 05:15:06 发布 · 176 阅读

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本文介绍了一种计算二叉树直径的方法，即找到二叉树中任意两节点间最长路径的长度，该路径可能经过也可能不经过根节点。通过递归获取每个节点的左右子树高度，以此来更新最长路径。

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 longestpath between any two nodes in a tree. This path may or may not pass through the root.

Example:
Given a binary tree

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.

这道题求二叉树的直径，并说明直径就是两点之间的最远距离，只要对每一个结点求出其左右子树深度之和，再加上1就可以更新结果res了。为了减少重复计算，可以用哈希表建立每个结点和其深度之间的映射，这样某个结点的深度之前计算过了，就不用再次计算了，参见代码如下：

class Solution {
public:
    int diameterOfBinaryTree(TreeNode* root) {
        if (!root) return 0;
        int res = getHeight(root->left) + getHeight(root->right);
        return max(res, max(diameterOfBinaryTree(root->left), diameterOfBinaryTree(root->right)));
    }
    int getHeight(TreeNode* node) {
        if (!node) return 0;
        if (m.count(node)) return m[node];
        int h = 1 + max(getHeight(node->left), getHeight(node->right));
        return m[node] = h;
    }

private:
    unordered_map<TreeNode*, int> m;
};