二叉树的非递归遍历

参考http://www.cnblogs.com/dolphin0520/archive/2011/08/25/2153720.html 的5楼回复

#include <iostream>
#include <stack>
using namespace std;

struct Node {
  int data;
  Node *left;
  Node *right;

  Node(int d, Node *l = NULL, Node *r = NULL){
    data = d;
    left = l;
    right = r;
  }
};

void preOrder(Node *root){
  if (!root)
    return;
  stack<Node *> s;
  s.push(root);

  while (!s.empty()) {
    Node *p = s.top();
    s.pop();
    cout << p->data << '\t';

    if (p->right != NULL)
      s.push(p->right);
    if (p->left != NULL)
      s.push(p->left);
  }
}

void inOrder(Node *root){
  if (!root)
    return;
  stack<pair<Node *, bool> > s;
  s.push(make_pair(root, false));

  while (!s.empty()) {
    Node *p = s.top().first;
    bool flag = s.top().second;
    s.pop();

    if (!flag) {
      if (p->right != NULL)
        s.push(make_pair(p->right, false));
      s.push(make_pair(p, true));
      if (p->left != NULL)
        s.push(make_pair(p->left, false));
    }
    else {
      cout << p->data << '\t';
    }
  }
}

void postOrder(Node *root)
{
  if (!root)
    return;
  stack<pair<Node *, bool> > s;
  s.push(make_pair(root, false));

  while (!s.empty()) {
    Node *p = s.top().first;
    bool flag = s.top().second;
    s.pop();

    if (!flag) {
      s.push(make_pair(p, true));
      if (p->right != NULL)
        s.push(make_pair(p->right, false));
      if (p->left != NULL)
        s.push(make_pair(p->left, false));
    }
    else {
      cout << p->data << '\t';
    }
  }
}

int main()
{
  Node *tmp;
  Node *root = new Node(1);
  tmp = new Node(2);
  root->left = tmp;
  tmp = new Node(3);
  root->right = tmp;
  tmp = new Node(4);
  root->left->left = tmp;
  tmp =  new Node(5);
  root->left->right = tmp;
  tmp = new Node(6);
  root->left->right->left = tmp;
  tmp = new Node(7);
  root->left->right->right = tmp;

  preOrder(root);
  cout << endl;
  inOrder(root);
  cout << endl;
  postOrder(root);
  cout << endl;

  int ttt = 0;
  return 0;
}