Leetcode二叉树的前、中、后序遍历_leetcode 实现二叉树先序,中序和后序遍历-优快云博客

Every day a leetcode

递归实现二叉树的前、中、后序遍历。

前序遍历

代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */


/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
#define MAX_NODE_SIZE 100
void preOrder(struct TreeNode* root,int* ans,int* ansSize)
{
    if(root == NULL) return;
    ans[(*ansSize)++]=root->val;
    preOrder(root->left,ans,ansSize);
    preOrder(root->right,ans,ansSize);
}
int* preorderTraversal(struct TreeNode* root, int* returnSize){
    *returnSize=0;
    int* ans=malloc(MAX_NODE_SIZE*sizeof(int));
    preOrder(root,ans,returnSize);
    return ans;
}

结果：
在这里插入图片描述

中序遍历

题目来源：94. 二叉树的中序遍历

代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */


/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
#define MAX_NODE_SZIE 100
void inOrder(struct TreeNode* root,int* ans,int* ansSize)
{
    if(root == NULL) return;
    inOrder(root->left,ans,ansSize);
    ans[(*ansSize)++]=root->val;
    inOrder(root->right,ans,ansSize);
}
int* inorderTraversal(struct TreeNode* root, int* returnSize){
    *returnSize=0;
    int *ans=malloc(MAX_NODE_SZIE*sizeof(int));
    inOrder(root,ans,returnSize);
    return ans;
}

结果：
在这里插入图片描述

后序遍历

题目来源：145. 二叉树的后序遍历

代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */


/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
#define MAX_NODE_SZIE 100
void postOrder(struct TreeNode* root,int* ans,int* ansSize)
{
    if(root == NULL) return;
    postOrder(root->left,ans,ansSize);
    postOrder(root->right,ans,ansSize);
    ans[(*ansSize)++]=root->val;
}
int* postorderTraversal(struct TreeNode* root, int* returnSize){
    *returnSize=0;
    int *ans=malloc(MAX_NODE_SZIE*sizeof(int));
    postOrder(root,ans,returnSize);
    return ans;
}