144.二叉树的前序遍历(opens new window)

要注意下创建函数参数传递不是很理解

class Solution {
public:void tranversal(TreeNode* s, vector<int> &b) {if (s == NULL) {return;}b.push_back(s->val);tranversal(s->left, b);tranversal(s->right, b);}vector<int> preorderTraversal(TreeNode* root) {vector <int> result;tranversal(root, result);return result;}
};

v.push_back(1); //v里面是1

v.push_back(2); //v里面是1 , 2

v.push_back(3); //v里面是1 , 2 , 3。

class Solution {
public:vector<int> preorderTraversal(TreeNode* root) {//stack<TreeNode> tmp;stack<TreeNode*> tmp;vector<int> result;if (root == NULL) return result;tmp.push(root);          //先把第一个父节点输入进去while(tmp.empty() == 0) { //当stack里面为空的时候就是元素都输出完毕了TreeNode * node = tmp.top(); //这句在后面的子节点就是弹出中间的数tmp.pop();result.push_back(node->val);if (node->right) tmp.push(node->right);           // 右（空节点不入栈）if (node->left) tmp.push(node->left);             // 左（空节点不入栈）}return result;}
};