二叉树的非递归遍历（栈）

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struct TreeNode{    int val;    TreeNode *left,*right;    TreeNode(int x):val(x),left(0),right(0){}};//前序遍历vector<int> preorderTraversal(TreeNode *root) {    vector<int> res;    stack<TreeNode *> s;    TreeNode *p=root;    while(!s.empty()||p)     {        while(p)        {            res.push_back(p->val);            s.push(p);            p=p->left;        }        if(!s.empty())        {            p=s.top();            s.pop();            p=p->right;        }    }    return res;}vector<int> preorderTraversal(TreeNode *root) {    vector<int> res;    stack<TreeNode *> s;    TreeNode *p=root;    while(!s.empty()||p)     {        if(p)        {            res.push_back(p->val);            s.push(p);            p=p->left;        }        else        {            p=s.top();            s.pop();            p=p->right;        }    }    return res;}//中序遍历vector<int> inorderTraversal(TreeNode *root) {    vector<int> res;    stack<TreeNode *> s;    TreeNode *p=root;    while(!s.empty()||p)     {        while(p)        {            s.push(p);            p=p->left;        }        if(!s.empty())           {            p=s.top();            s.pop();            res.push_back(p->val);            p=p->right;        }    }    return res;}vector<int> inorderTraversal(TreeNode *root) {    vector<int> res;    stack<TreeNode *> s;    TreeNode *p=root;    while(!s.empty()||p)     {        if(p)        {            s.push(p);            p=p->left;        }        else           {            p=s.top();            s.pop();            res.push_back(p->val);            p=p->right;        }    }    return res;}//后序遍历vector<int> postorderTraversal(TreeNode *root) {    vector<int> res;    stack<TreeNode *> s;    TreeNode *cur=root,*prev=0;    while(cur)      {          s.push(cur);          cur=cur->left;      }    while(!s.empty())      {           cur=s.top();          s.pop();            if(!cur->right||cur->right==prev)          {              res.push_back(cur->val);             prev=cur;          }          else          {                s.push(cur);                cur=cur->right;              while(cur)              {                  s.push(cur);                  cur=cur->left;              }          }      }      return res;}
http://blog.csdn.net/zhangxiangdavaid/article/details/37115355
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