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