2015-10-18 10:42:52 +08:00

150 lines
3.1 KiB
C++

// Source : https://oj.leetcode.com/problems/binary-tree-preorder-traversal/
// Author : Hao Chen
// Date : 2014-07-21
/**********************************************************************************
*
* Given a binary tree, return the preorder traversal of its nodes' values.
*
* For example:
* Given binary tree {1,#,2,3},
*
* 1
* \
* 2
* /
* 3
*
* return [1,2,3].
*
* Note: Recursive solution is trivial, could you do it iteratively?
*
**********************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <iostream>
#include <vector>
using namespace std;
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
vector<int> preorderTraversal1(TreeNode *root);
vector<int> preorderTraversal2(TreeNode *root);
vector<int> preorderTraversal(TreeNode *root) {
if (random()%2){
cout << "---method one---" << endl;
return preorderTraversal1(root);
}
cout << "---method two---" << endl;
return preorderTraversal2(root);
}
vector<int> preorderTraversal1(TreeNode *root) {
vector<int> v;
vector<TreeNode*> stack;
if (root) {
stack.push_back(root);
}
while (stack.size()>0){
TreeNode* n = stack.back();
v.push_back(n->val);
stack.pop_back();
if (n->right){
stack.push_back(n->right);
}
if (n->left){
stack.push_back(n->left);
}
}
return v;
}
vector<int> preorderTraversal2(TreeNode *root) {
vector<int> v;
vector<TreeNode*> stack;
stack.push_back((TreeNode*)NULL);
TreeNode *top = root;
while(top!=NULL){
v.push_back(top->val);
if (top->right !=NULL){
stack.push_back(top->right);
}
if (top->left != NULL){
stack.push_back(top->left);
}
top = stack.back();
stack.pop_back();
}
return v;
}
TreeNode* createTree(int a[], int n)
{
if (n<=0) return NULL;
TreeNode **tree = new TreeNode*[n];
for(int i=0; i<n; i++) {
if (a[i]==0 ){
tree[i] = NULL;
continue;
}
tree[i] = new TreeNode(a[i]);
}
int pos=1;
for(int i=0; i<n && pos<n; i++) {
if (tree[i]){
tree[i]->left = tree[pos++];
if (pos<n){
tree[i]->right = tree[pos++];
}
}
}
return tree[0];
}
void printTree_pre_order(TreeNode *root)
{
if (root == NULL){
//cout << "# ";
return ;
}
cout << root->val << " ";
printTree_pre_order(root->left);
printTree_pre_order(root->right);
}
void printArray(vector<int> v)
{
for(int i=0; i<v.size(); i++){
cout << v[i] << " ";
}
cout << endl;
}
int main()
{
srand(time(0));
int a[] = {1,2,3,4,5,0,6,0,0,7,8,9,0};
TreeNode* p = createTree(a, sizeof(a)/sizeof(int));
printTree_pre_order(p);
cout << endl;
vector<int> v = preorderTraversal(p);
printArray(v);
cout << endl;
return 0;
}