【LeetCode热题100（48/100）】二叉树的最近公共祖先

题目地址：链接

思路： 后序遍历递归查找，标记左右子树是否包含目标节点，首次同时满足的节点即为最近公共祖先。

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @param {TreeNode} p
 * @param {TreeNode} q
 * @return {TreeNode}
 */
var lowestCommonAncestor = function(root, p, q) {
    let ans = root;
    let flag = true;
    const dfs = (root, l, r) => {
        if(!root) return [l, r];
        if(l && r) return [l, r];


        let [ll, rl] = dfs(root.left, l, r);
        let [lr, rr] = dfs(root.right, l, r);

        l = l || ll || lr;
        r = r || rl || rr;
        if(p == root) l = true;
        if(q == root) r = true;
        
        if((l || ll || lr) && (r || rl || rr) && flag) {
            ans = root;
            flag = false;
        }
    
        return [l, r]
    }
    dfs(root, false, false)
    return ans;
};