# 1740. Find Distance in a Binary Tree
###### tags: `Leetcode` `Medium` `Tree` `LCA`
Link: https://leetcode.com/problems/find-distance-in-a-binary-tree/
## 思路
和其他LCA的题差不多 稍微有一点变式
在findLCA里面 如果回传-1 说明当下subtree里面没有p/q或者已经找到答案了
## Code

class Solution {
    int result = 0;
    public int findDistance(TreeNode root, int p, int q) {
        if(p==q) return 0;
        findLCA(root, p, q);
        return result;
    }
    private int findLCA(TreeNode root, int p, int q){
        if(root==null) return -1;
        int left = findLCA(root.left, p, q);
        int right = findLCA(root.right, p, q);
        if(root.val==p || root.val==q){
            if (left < 0 && right < 0) {
                return 0;
            }
            result = 1 + (left >= 0 ? left : right);
            return -1;
        }
        if(left>=0 && right>=0){
            result = left+right+2;
            return -1;
        }
        else if(left>=0) return left+1;
        else if(right>=0) return right+1;
        else return -1;
    }
}