LeetCode 236. Lowest Common Ancestor of a Binary Tree | DFS | Python C++

Python

class Solution:
    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
        if root in [None, p, q]: return root
        left = self.lowestCommonAncestor(root.left, p, q)
        right = self.lowestCommonAncestor(root.right, p, q)
        return root if left and right else left or right 

两种情况
1.单边找到
a.已经p and q都找到，返回之前的答案
b.只找到一边，是需要update node但是可以在两边找到的时候完成
2.两边找到，当前node

C++

class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(!root || root==p || root==q) return root;
        TreeNode* l = lowestCommonAncestor(root->left, p, q);
        if(l && l!=p && l!=q) return l;
        TreeNode* r = lowestCommonAncestor(root->right, p, q);
        if(r && r!=p && r!=q) return r;
        if(l && r) return root;
        return l?l:r;
    }
};