二叉树的最大深度算法面试题-leetcode学习之旅（3）

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标题

Maximum Depth of Binary Tree

描述

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

c++实现方法代码

1.递归实现，时间复杂度为O(n) 空间复杂度为O（logn）

/** * 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(root == NULL){            return 0;        }        int left = maxDepth(root->left);        int right = maxDepth(root->right);        return 1 + max(left,right);    }};

2.队列实现

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    //二叉树最大深度（层次遍历，遍历一层高度加1）    int maxDepth(TreeNode *root) {        int height = 0,rowCount = 1;        if(root == NULL){            return 0;        }        //创建队列        queue<treenode*> queue;        //添加根节点        queue.push(root);        //层次遍历        while(!queue.empty()){            //队列头元素            TreeNode *node = queue.front();            //出队列            queue.pop();            //一层的元素个数减1，一层遍历完高度加1            rowCount --;            if(node->left){                queue.push(node->left);            }            if(node->right){                queue.push(node->right);            }            //一层遍历完            if(rowCount == 0){                //高度加1                height++;                //下一层元素个数                rowCount = queue.size();            }        }        return height;    }};</treenode*>

3.栈

/** * 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) {          // Start typing your C/C++ solution below          // DO NOT write int main() function          if(root == NULL) return 0;          stack<treenode*> S;          int maxDepth = 0;          TreeNode *prev = NULL;          S.push(root);          while (!S.empty()) {              TreeNode *curr = S.top();              if (prev == NULL || prev->left == curr || prev->right == curr) {                  if (curr->left)                      S.push(curr->left);                  else if (curr->right)                      S.push(curr->right);              } else if (curr->left == prev) {                  if (curr->right)                      S.push(curr->right);              } else {                  S.pop();              }              prev = curr;              if (S.size() > maxDepth)                  maxDepth = S.size();          }          return maxDepth;      }  };</treenode*>

4.测试

**********************************/#include <iostream>#include <malloc.h>#include <stdio.h>using namespace std;typedef struct TreeNode{    int val;    TreeNode *left;    TreeNode *right;    TreeNode(int x) : val(x), left(NULL), right(NULL) {}}TreeNode,*BiTree;//按先序序列创建二叉树int CreateBiTree(BiTree &T){    int data;    //按先序次序输入二叉树中结点的值，‘-1’表示空树    scanf("%d",&data);    if(data == -1){        T = NULL;    }    else{        T = (BiTree)malloc(sizeof(TreeNode));        //生成根结点        T->val = data;        //构造左子树        CreateBiTree(T->left);        //构造右子树        CreateBiTree(T->right);    }    return 0;}//二叉树最大深度（递归）int maxDepth(TreeNode *root) {    if(root == NULL){        return 0;    }    int left = maxDepth(root->left);    int right = maxDepth(root->right);    return 1 + max(left,right);}int main() {    int i,n;    BiTree T = NULL;    CreateBiTree(T);    printf("%d\n",maxDepth(T));    return 0;}</stdio.h></malloc.h></iostream>

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