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1740. 找到二叉树中的距离 🔒

题目描述

给定一棵二叉树的根节点 root 以及两个整数 p 和 q ，返回该二叉树中值为 p 的结点与值为 q 的结点间的 距离 。

两个结点间的 距离 就是从一个结点到另一个结点的路径上边的数目。

 

示例 1：

输入：root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 0
输出：3
解释：在 5 和 0 之间有 3 条边：5-3-1-0

示例 2：

输入：root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 7
输出：2
解释：在 5 和 7 之间有 2 条边：5-2-7

示例 3：

输入：root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 5
输出：0
解释：一个结点与它本身之间的距离为 0

 

提示：

  • 树中结点个数的范围在 [1, 104].
  • 0 <= Node.val <= 109
  • 树中所有结点的值都是唯一的.
  • p 和q 是树中结点的值.

解法

方法一

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# 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 findDistance(self, root: Optional[TreeNode], p: int, q: int) -> int:
        def lca(root, p, q):
            if root is None or root.val in [p, q]:
                return root
            left = lca(root.left, p, q)
            right = lca(root.right, p, q)
            if left is None:
                return right
            if right is None:
                return left
            return root

        def dfs(root, v):
            if root is None:
                return -1
            if root.val == v:
                return 0
            left, right = dfs(root.left, v), dfs(root.right, v)
            if left == right == -1:
                return -1
            return 1 + max(left, right)

        g = lca(root, p, q)
        return dfs(g, p) + dfs(g, q)

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/**
 * 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 findDistance(TreeNode root, int p, int q) {
        TreeNode g = lca(root, p, q);
        return dfs(g, p) + dfs(g, q);
    }

    private int dfs(TreeNode root, int v) {
        if (root == null) {
            return -1;
        }
        if (root.val == v) {
            return 0;
        }
        int left = dfs(root.left, v);
        int right = dfs(root.right, v);
        if (left == -1 && right == -1) {
            return -1;
        }
        return 1 + Math.max(left, right);
    }

    private TreeNode lca(TreeNode root, int p, int q) {
        if (root == null || root.val == p || root.val == q) {
            return root;
        }
        TreeNode left = lca(root.left, p, q);
        TreeNode right = lca(root.right, p, q);
        if (left == null) {
            return right;
        }
        if (right == null) {
            return left;
        }
        return root;
    }
}

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/**
 * 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 findDistance(TreeNode* root, int p, int q) {
        TreeNode* g = lca(root, p, q);
        return dfs(g, p) + dfs(g, q);
    }

    TreeNode* lca(TreeNode* root, int p, int q) {
        if (!root || root->val == p || root->val == q) return root;
        TreeNode* left = lca(root->left, p, q);
        TreeNode* right = lca(root->right, p, q);
        if (!left) return right;
        if (!right) return left;
        return root;
    }

    int dfs(TreeNode* root, int v) {
        if (!root) return -1;
        if (root->val == v) return 0;
        int left = dfs(root->left, v);
        int right = dfs(root->right, v);
        if (left == -1 && right == -1) return -1;
        return 1 + max(left, right);
    }
};

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/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func findDistance(root *TreeNode, p int, q int) int {
    var lca func(root *TreeNode, p int, q int) *TreeNode
    lca = func(root *TreeNode, p int, q int) *TreeNode {
        if root == nil || root.Val == p || root.Val == q {
            return root
        }
        left, right := lca(root.Left, p, q), lca(root.Right, p, q)
        if left == nil {
            return right
        }
        if right == nil {
            return left
        }
        return root
    }
    var dfs func(root *TreeNode, v int) int
    dfs = func(root *TreeNode, v int) int {
        if root == nil {
            return -1
        }
        if root.Val == v {
            return 0
        }
        left, right := dfs(root.Left, v), dfs(root.Right, v)
        if left == -1 && right == -1 {
            return -1
        }
        return 1 + max(left, right)
    }
    g := lca(root, p, q)
    return dfs(g, p) + dfs(g, q)
}

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