二叉树的非递归遍历

来源：互联网发布：windows version 1703 编辑：程序博客网时间：2024/06/07 09:30

先是中序遍历

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    vector<int> inorderTraversal(TreeNode *root) {        vector<int>v;        stack<TreeNode*>s;        TreeNode* p = root;        while(!s.empty() || p != NULL){            if(p != NULL){                s.push(p);                p = p->left;            }else {                p = s.top();                s.pop();                v.push_back(p->val);                p = p->right;            }        }         return v;    }};

然后是前序遍历

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    vector<int> preorderTraversal(TreeNode *root) {         vector<int>v;         if(root == NULL) return v;         stack<TreeNode*>s;         s.push(root);         while(!s.empty()){             TreeNode *tmp = s.top();              s.pop();             v.push_back(tmp->val);             if(tmp->right) s.push(tmp->right);             if(tmp->left) s.push(tmp->left);         }         return v;    }};

后序遍历

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    vector<int> postorderTraversal(TreeNode *root) {          stack<TreeNode*>s;          vector<int>ans;          if(root == NULL) return ans;             TreeNode *p = root, *q;          do{             while(p){                s.push(p);                p = p->left;             }           q = NULL;            while(!s.empty()){                p = s.top();                s.pop();                if(p->right == q){                   ans.push_back(p->val);                   q = p;                }else {                    s.push(p);                    p = p->right;                    break;                }            }          }while(!s.empty());          return ans;    }};

vector<int> postorderTraversal(TreeNode *root) {    vector<int> v;    if (!root) return v;    stack<TreeNode *> s;    s.push(root);    TreeNode *p = NULL;    while(!s.empty()) {        p = s.top();        s.pop();        v.insert(v.begin(), p->val);        if (p->left) s.push(p->left);        if (p->right) s.push(p->right);    }    return v;}

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