个人技术分享

144.二叉树的前序遍历

递归遍历代码如下：

class Solution {
public:
    void preOrder(TreeNode *root, vector<int> &vec){
        if(root == NULL) return;
        vec.push_back(root->val);
        preOrder(root->left, vec);
        preOrder(root->right, vec);
    }
    vector<int> preorderTraversal(TreeNode* root) {
        vector<int> result;
        preOrder(root, result);
        return result;
    }
};

迭代遍历代码如下：

class Solution {
public:
    vector<int> preorderTraversal(TreeNode* root) {
        vector<int> result;
        stack<TreeNode*> myStack;
        if(root == NULL) return result;
        myStack.push(root);
        while(!myStack.empty()){
            TreeNode* root = myStack.top();
            myStack.pop();
            result.push_back(root->val);
            if(root->right) myStack.push(root->right);
            if(root->left) myStack.push(root->left);
        }
        return result;
    }
};

统一迭代遍历：

代码如下：

class Solution {
public:
    vector<int> preorderTraversal(TreeNode* root) {
        vector<int> result;
        stack<TreeNode*> st;
        if(root != NULL) st.push(root);;
        while(!st.empty()){
            TreeNode* node = st.top();
            if(node != NULL){
                st.pop();
                if(node->right) st.push(node->right);
                if(node->left) st.push(node->left);
                st.push(node);
                st.push(NULL);
            }
            else{
                st.pop();
                node = st.top();
                st.pop();
                result.push_back(node->val);
            }
        }
        return result;
    }
};

145.二叉树的后序遍历

递归遍历代码如下：

class Solution {
public:
    void postOrder(TreeNode* root, vector<int> &vec){
        if(root == NULL) return;
        postOrder(root->left, vec);
        postOrder(root->right, vec);
        vec.push_back(root->val);
    }
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> result;
        postOrder(root, result);
        return result;
    }
};

迭代遍历代码如下：

想不到，抄得很爽

class Solution {
public:
    vector<int> postorderTraversal(TreeNode *root){
        vector<int> result;
        stack<TreeNode*> st;
        if(root == NULL) return result;
        st.push(root);
        while(!st.empty()){
            root = st.top();
            st.pop();
            result.push_back(root->val);
            if(root->left) st.push(root->left);
            if(root->right) st.push(root->right);
        }
        reverse(result.begin(), result.end());
        return result;
    }
};

统一迭代遍历:

似懂非懂，抄得很爽，代码如下：

class Solution {
public:
    vector<int> postorderTraversal(TreeNode *root){
        vector<int> result;
        stack<TreeNode*> st;
        if(root != NULL) st.push(root);;
        while(!st.empty()){
            TreeNode* node = st.top();
            if(node != NULL){
                st.pop();
                st.push(node);
                st.push(NULL);
                if(node->right) st.push(node->right);
                if(node->left) st.push(node->left);
            }
            else{
                st.pop();
                node = st.top();
                st.pop();
                result.push_back(node->val);
            }
        }
        return result;
    }
};

94.二叉树的中序遍历

递归遍历代码如下：

class Solution {
public:
    void inOrder(TreeNode *root, vector<int>& vec){
        if(root == NULL) return;
        inOrder(root->left, vec);
        vec.push_back(root->val);
        inOrder(root->right, vec);
    }
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> result;
        inOrder(root, result);
        return result;
    }
};

迭代遍历代码如下：

想不出，抄得很爽。。

class Solution {
public:
    vector<int> inorderTraversal(TreeNode* root){
        vector<int> result;
        stack<TreeNode*> st;
        TreeNode* cur = root;
        while(cur != NULL || !st.empty()){
            if(cur != NULL){
                st.push(cur);
                cur = cur->left;
            }
            else{
                cur = st.top();
                result.push_back(cur->val);
                st.pop();
                cur = cur->right;
            }
        }
        return result;
    }
};

统一迭代遍历：

狠狠地抄，代码如下：

class Solution {
public:
    vector<int> inorderTraversal(TreeNode* root){
        vector<int> result;
        stack<TreeNode*> st;
        if(root != NULL) st.push(root);;
        while(!st.empty()){
            TreeNode* node = st.top();
            if(node != NULL){
                st.pop();
                if(node->right) st.push(node->right);
                st.push(node);
                st.push(NULL);
                if(node->left) st.push(node->left);
            }
            else{
                st.pop();
                node = st.top();
                st.pop();
                result.push_back(node->val);
            }
        }
        return result;
    }
};

102.二叉树的层序遍历

好多题，今天就这样了。

代码如下：

class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> result;
        queue<TreeNode*> que;
        if(root != NULL) que.push(root);
        while(!que.empty()){
            int size = que.size();
            vector<int> miniResult;
            for(int i = 0; i < size; i++){
                TreeNode* node = que.front();
                que.pop();
                miniResult.push_back(node->val);
                if(node->left) que.push(node->left);
                if(node->right) que.push(node->right);
            }
            result.push_back(miniResult);
        }
        return result;
    }
};