leetcode代码分类汇总之-树

leetcode中关于树的题目汇总，这部分题目比较多：

Balanced Binary Tree

class Solution {
public:
    int subBal(TreeNode* root){
        if(root==NULL)
            return 0;
        int left = subBal(root->left);
        int right = subBal(root->right);
        if(left<0||right<0||abs(left-right)>1) return -1;
        return max(left,right)+1;
    }
    bool isBalanced(TreeNode *root) {
        return subBal(root)>=0;
    }
};

Binary Tree Inorder Traversal

这个给出两种实现，第一种是网上的，第二种是用我说的比较通用的转化方法做的：

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

class Solution {
public:
    struct Node{
        TreeNode* node_;
        bool sign;
        Node(TreeNode* n){node_=n;sign=false;}
    };
    vector inorderTraversal(TreeNode *root) {
        stack stk;
        stk.push(Node(root));
        vector result;
        if(!root) return result;
        while(!stk.empty()){
            Node tmp = stk.top();
            stk.top().sign = true;
            if(tmp.sign){
                result.push_back(tmp.node_->val);
                stk.pop();
                if(tmp.node_->right)
                  stk.push(Node(tmp.node_->right));
            }else if(tmp.node_->left)
              stk.push(Node(tmp.node_->left));
        }
        return result;
    }
};

Binary Tree Level Order Traversal

public:
    vector > levelOrder(TreeNode *root) {
        TreeNode* pre_level = root;
        vector> result;
        if(!root) return result;
        queue q;
        q.push(root);
        result.push_back(vector());
        while(!q.empty()){
            TreeNode* node = q.front();
            q.pop();
            result.back().push_back(node->val);
            if(node->left) q.push(node->left);
            if(node->right) q.push(node->right);
            if(pre_level==node){
                pre_level = q.back();
                result.push_back(vector());
            }
        }
        result.pop_back();
        return result;
    }
};

Binary Tree Level Order Traversal II

class Solution {
public:
    void RecBottom(TreeNode* root,vector>& result,int level){
        if(!root) return;
        result[result.size()-1-level].push_back(root->val);
        RecBottom(root->left,result,level+1);
        RecBottom(root->right,result,level+1);
    }
    int MaxHeight(TreeNode* root,int d){
        if(!root) return d;
        return max(MaxHeight(root->left,d+1),MaxHeight(root->right,d+1));
    }
    vector > levelOrderBottom(TreeNode *root) {
        int height = MaxHeight(root,0);
        vector> result(height);
        RecBottom(root,result,0);
        return result;
    }
};

Binary Tree Maximum Path Sum

class Solution {
public:
    int findMaxSum(TreeNode* root,int& pathMax,int& maxNode){
        if(root==NULL){
            pathMax = 0;
            return 0;
        }
        if(root->val>maxNode) maxNode = root->val;
        int left,right,leftPath,rightPath;
        left = findMaxSum(root->left,leftPath,maxNode);
        right = findMaxSum(root->right,rightPath,maxNode);
        pathMax = max(max(leftPath,rightPath)+root->val,0);
        return max(max(left,right),leftPath+rightPath+root->val);
    }
    int maxPathSum(TreeNode *root) {
        if(root==NULL) return 0;
        int m,maxNode=root->val;
        int ans = findMaxSum(root,m,maxNode);
        if(ans==0) return maxNode;
        return ans;
    }
};

Binary Tree Zigzag Level Order Traversal

class Solution {
public:
    vector > zigzagLevelOrder(TreeNode *root) {
        vector> ans;
        if(root==NULL) return ans;
        queue q;
        q.push(root);
        TreeNode* pre = root;
        vector nowVec;
        ans.push_back(nowVec);
        while(!q.empty()){
            TreeNode* tmp = q.front();
            q.pop();
            ans[ans.size()-1].push_back(tmp->val);
            if(tmp->left!=NULL) q.push(tmp->left);
            if(tmp->right!=NULL) q.push(tmp->right);
            if(tmp==pre){
                ans.push_back(nowVec);
                if(!q.empty())
                    pre = q.back();
            }
        }
        ans.pop_back();
        for(int i=1;i

===============================树题目还有很多，果断时间再补上===============================