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<int> inorderTraversal(TreeNode *root) {        vector<int> ans;        if(root==NULL) return ans;        stack<TreeNode*> 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<int> inorderTraversal(TreeNode *root) {        stack<Node> stk;        stk.push(Node(root));        vector<int> 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<vector<int> > levelOrder(TreeNode *root) {        TreeNode* pre_level = root;        vector<vector<int>> result;        if(!root) return result;        queue<TreeNode*> q;        q.push(root);        result.push_back(vector<int>());        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<int>());            }        }        result.pop_back();        return result;    }};

Binary Tree Level Order Traversal II

class Solution {public:    void RecBottom(TreeNode* root,vector<vector<int>>& 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<vector<int> > levelOrderBottom(TreeNode *root) {        int height = MaxHeight(root,0);        vector<vector<int>> 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<vector<int> > zigzagLevelOrder(TreeNode *root) {        vector<vector<int>> ans;        if(root==NULL) return ans;        queue<TreeNode*> q;        q.push(root);        TreeNode* pre = root;        vector<int> 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<ans.size();i+=2)            for(int j=0,k=ans[i].size()-1;j<k;)                std::swap(ans[i][j++],ans[i][k--]);        return ans;    }};

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