Solution.cpp

#include <unistd.h>
#include <assert.h>
#include <stdio.h>

struct TreeNode
{
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Solution
{
public://https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/discuss/65225/4-lines-C%2B%2BJavaPythonRuby
    TreeNode *lowestCommonAncestor(TreeNode *root, TreeNode *p, TreeNode *q)
    {
        if (!root || root == p || root == q)
            return root;
        TreeNode *left = lowestCommonAncestor(root->left, p, q);
        TreeNode *right = lowestCommonAncestor(root->right, p, q);
        return !left ? right : !right ? left : root;
    }
};

int main(int argc, char const *argv[])
{
    TreeNode n0 = TreeNode(0);
    TreeNode n8 = TreeNode(8);
    TreeNode n1 = TreeNode(1);
    n1.left = &n0;
    n1.right = &n8;
    TreeNode n4 = TreeNode(4);
    TreeNode n7 = TreeNode(7);
    TreeNode n2 = TreeNode(2);
    n2.left = &n7;
    n2.right = &n4;
    TreeNode n6 = TreeNode(6);
    TreeNode n5 = TreeNode(5);
    n5.left = &n6;
    n5.right = &n2;
    TreeNode n3 = TreeNode(3);
    n3.left = &n5;
    n3.right = &n1;
    Solution a;
    TreeNode *x = a.lowestCommonAncestor(&n3, &n5, &n1);
    assert(x == &n3);
    TreeNode *y = a.lowestCommonAncestor(&n3, &n5, &n4);
    assert(y == &n5);
    printf("success");
    return 0;
}