144. 二叉树的前序遍历

C代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
/**
 * Return an array of size *returnSize.
 * Note: The returned array must be malloced, assume caller calls free().
 */

void visit(struct TreeNode* root, int **result,int* returnSize){
    if(!*result){
        *result=(int *)malloc(sizeof(int));
    }else{
        *result=(int *)realloc(*result,((*returnSize)+1)*sizeof(int));
    }
    (*result)[(*returnSize)++]=root->val;
}
void preOrder(struct TreeNode* root, int **result,int* returnSize){
    if(root){
        visit(root,result,returnSize);
        preOrder(root->left,result,returnSize);
        preOrder(root->right,result,returnSize);
    }
}
int* preorderTraversal(struct TreeNode* root, int* returnSize) {
    int *result=NULL;
    preOrder(root,&result,returnSize);
    return result;
}

Java代码：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

class Solution {

    // 访问节点并存储
    public void visit(TreeNode root, List<Integer> result) {
        // 在Java中这个函数实现起来就省事了很多，不用像C语言那样临时分配内存
        result.add(root.val);
    }

    // 先序
    public void preOder(TreeNode root, List<Integer> result) {
        if (root != null) {
            visit(root, result);
            preOder(root.left, result);
            preOder(root.right, result);
        }
    }

    public List<Integer> preorderTraversal(TreeNode root) {
        List<Integer> result = new ArrayList<Integer>();
        preOder(root, result);
        return result;
    }
}