LCA of Deepest Nodes in Binary Tree - Facebook


https://www.cnblogs.com/EdwardLiu/p/6551606.html
给一个 二叉树 , 求最深节点的最小公共父节点
     1
  2   3
     5  6    return 3.

       1  
    2   3
4      5 6   retrun 1. 
先用 recursive  , 很快写出来了, 要求用 iterative 。 时间不够了。。。
复制代码
Recursion: 返回的时候返回lca和depth每个node如果有大于一个子节点的depth相同就返回这个node,如果有一个子节点depth更深就返回个子节点lca,这个o(n)就可以了
Iteration: tree的recursion换成iteration处理,一般用stack都能解决吧(相当于手动用stack模拟recursion)。感觉这题可以是一个样的做法,换成post order访问,这样处理每个node的时候,左右孩子的信息都有了,而且最后一个处理的node一定是tree root
我的想法是要用hashMap<TreeNode, Info>
class Info{
  int height;
  TreeNode LCA;
}

 5     private class ReturnVal {
 6         public int depth;   //The depth of the deepest leaves on the current subtree
 7         public TreeNode lca;//The lca of the deepest leaves on the current subtree
 8 
 9         public ReturnVal(int d, TreeNode n) {
10             depth = d;
11             lca = n;
12         }
13     }
14 
15     public TreeNode LowestCommonAncestorOfDeepestLeaves(TreeNode root) {
16         ReturnVal res = find(root);
17         return res.lca;
18     }
19 
20     private ReturnVal find(TreeNode root) {
21         if(root == null) {
22             return new ReturnVal(0, null);
23         } else {
24             ReturnVal lRes = find(root.left);
25             ReturnVal rRes = find(root.right);
26 
27             if(lRes.depth == rRes.depth) {
28                 return new ReturnVal(lRes.depth+1, root);
29             } else {
30                 return new ReturnVal(Math.max(rRes.depth, lRes.depth)+1, rRes.depth>lRes.depth?rRes.lca:lRes.lca);
31             }
32         }
33     }

find lowest common ancestor among deepest nodes in k-nary tree
前⼏几年年的经典题


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