LeetCode 104. Maximum Depth of Binary Tree

題目

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

翻譯

找出一個二元樹的深度。

範例：

Tree1 depth = 3               Tree2 depth = 4 
   A                           3
  / \                         / \
 B   C                       4   4
    / \                     /  
   D   E                   2
                          /
                         3

   fn(n) = 0, if null;  
   fn(n) = 1 + max(f(n.left), f(n.right))　


以上面tree1為例  
*nodeA的深度 = 1 + max (nodeB深度 , nodeC深度) // B，C取深度較深的 
*nodeB 沒有子節點，nodeB depth = 1  
*nodeC 有子節點[D,E]，nodeB depth = 2    
*nodeA depth = 1 + 2 = 3

解題

var maxDepth = function(root) {
    return find(root); 
    // 遞迴函式
    function find(node){
        // 節點到底
        if(node === null){
            return 0;
        } 

        var deepL = 1;
        var deepR = 1;
        // 有左節點，往下一層找
        if(node.left !== null){
            deepL += find(node.left)
        }
        // 有右節點，往下一層找
        if(node.right !== null){
            deepR += find(node.right)
        }

        // 回傳較大的深度depth，給上一層節點
        return deepL > deepR ?　deepL: deepR;
    }
};