[LeetCode] Maximum Depth of Binary Tree

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.

 

分析：就是传统意义上的二叉树高度

1 递归：

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode *root) {

    if (NULL == root) return 0;
    int leftHeight = maxDepth(root->left);
    int rightHeight = maxDepth(root->right);
    int height ;
    if(leftHeight > rightHeight)
        height = leftHeight;
    else
        height = rightHeight;
    return height + 1;
 
    }
};

 框架和求最小深度一样的非递归，由于最大长度要遍历到所有也节点，所以没有减枝

struct newNode{
    TreeNode * node;
    int         dep;
};

class Solution {
    public:
        int maxDepth(TreeNode *root) {
            ;
            if(NULL == root) return 0;

            int maxDep = INT_MIN;

            stack<newNode*> stack;

            newNode *p = new newNode;
            p->node = root;
            p->dep = 1;
            stack.push(p);

            while( !stack.empty())
            {
                p= stack.top();
                stack.pop();

                TreeNode *pNode = p->node;
                int dep = p->dep;


                if(pNode->left == NULL && pNode->right == NULL)
                {
                    maxDep = max(maxDep, dep);
                }

                if(pNode->left != NULL)
                {
                    newNode *tmp = new newNode;
                    tmp->node = pNode->left;
                    tmp->dep = dep + 1;
                    stack.push(tmp);
                }

                if(pNode->right != NULL)
                {
                    newNode *tmp = new newNode;
                    tmp->node = pNode->right;
                    tmp->dep = dep + 1;
                    stack.push(tmp);
                }

            }

            return maxDep;
        }

};