二叉树定义

struct TreeNode
{
int val;
struct TreeNode *left;
struct TreeNode *right;
};

前序

主调函数

int* preorderTraversal(struct TreeNode* root, int* returnSize){
    int n=size(root);
    int *preorder_arry=(int*)malloc(sizeof(int)*n);
    *returnSize=n;

    int index=0;
//遍历
    _preorderTraversal(root,preorder_arry,&index);

    return preorder_arry;

}

returnSize对应二叉树节点大小；

返回节点个数

二叉树节点个数=左子树节点个数+右子树节点个数+1[if(root==NULL) return 0;]

int size(struct TreeNode*t)
{
    if(t==NULL)
    return 0;
    else
    return size(t->left)+size(t->right)+1;
}

二叉树以数组形式

void _preorderTraversal(struct TreeNode*root,int *preorder_arry,int *i)
{
    if(root!=NULL)
    {
        preorder_arry[*i]=root->val;
        (*i)++;
        _preorderTraversal(root->left,preorder_arry,i);
        _preorderTraversal(root->right,preorder_arry,i);
    }
}

中序

/**
 * 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().
 */
 //返回节点大小
 int size(struct TreeNode*t)
{
    if(t==NULL)
    return 0;
    else
    return size(t->left)+size(t->right)+1;
}

void _inorderTraversal(struct TreeNode*root,int *inorder_arry,int *i)
{
    if(root!=NULL)
    {
        _inorderTraversal(root->left,inorder_arry,i);
        inorder_arry[*i]=root->val;
        (*i)++;
        _inorderTraversal(root->right,inorder_arry,i);
    }
}


int* inorderTraversal(struct TreeNode* root, int* returnSize){

    int n=size(root);
    int *inorder_arry=(int*)malloc(sizeof(int)*n);
    *returnSize=n;

//遍历
    int index=0;
    _inorderTraversal(root,inorder_arry,&index);

    return inorder_arry;
}

后序：

/**
 * 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().
 */
int size(struct TreeNode*t)
{
    if(t==NULL)
    return 0;
    else
    return size(t->left)+size(t->right)+1;
}

void _postorderTraversal(struct TreeNode*root,int *postorder_arry,int *i)
{
    if(root!=NULL)
    {
        _postorderTraversal(root->left,postorder_arry,i);
        _postorderTraversal(root->right,postorder_arry,i);
        postorder_arry[*i]=root->val;
        (*i)++;
    }
}


int* postorderTraversal(struct TreeNode* root, int* returnSize){
    int n=size(root);
    int *postorder_arry=(int*)malloc(sizeof(int)*n);
    *returnSize=n;

//遍历
    int index=0;
    _postorderTraversal(root,postorder_arry,&index);

    return postorder_arry;
}