《慕课网玩转算法面试》笔记及习题解答6.4.~6.6

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leetcode 102

    vector<vector<int>> levelOrder(TreeNode* root) {        vector<vector<int>> res;        if(root == NULL)            return res;        //层序遍历        queue<pair<TreeNode*,int>> q;        //root作为第0层        q.push( make_pair(root,0) );        while(!q.empty()){            TreeNode* node = q.front().first;            int level = q.front().second;            //当level == res.size()时，说明res[level]为空，此时新建一个vector插入            if(level == res.size()){                vector<int> tmp;                tmp.push_back(node->val);                res.push_back(tmp);            }            else res[level].push_back(node->val);            if(node->left) q.push( make_pair(node->left ,level+1) );            if(node->right) q.push( make_pair(node->right ,level+1) );            q.pop();        }        return res;    }

练习：

leetcode 107

    vector<vector<int>> levelOrderBottom(TreeNode* root) {        vector<vector<int>> res;        if(root == NULL)            return res;        //层序遍历        queue<pair<TreeNode*,int>> q;        //root作为第0层        q.push( make_pair(root,0) );        while(!q.empty()){            TreeNode* node = q.front().first;            int level = q.front().second;            //当level == res.size()时，说明res[level]为空，此时新建一个vector插入            if(level == res.size()){                vector<int> tmp;                tmp.push_back(node->val);                res.push_back(tmp);            }            else res[level].push_back(node->val);            if(node->left) q.push( make_pair(node->left ,level+1) );            if(node->right) q.push( make_pair(node->right ,level+1) );            q.pop();        }        reverse(res.begin(), res.end());        return res;     }

leetcode 103

    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {        vector<vector<int>> res;        if(root == NULL)            return res;        //层序遍历        queue<pair<TreeNode*,int>> q;        //root作为第0层        q.push( make_pair(root,0) );        while(!q.empty()){            TreeNode* node = q.front().first;            int level = q.front().second;            //当level == res.size()时，说明res[level]为空，此时新建一个vector插入            if(level == res.size()){                vector<int> tmp;                tmp.push_back(node->val);                res.push_back(tmp);            }            else res[level].push_back(node->val);            if(node->left) q.push( make_pair(node->left ,level+1) );            if(node->right) q.push( make_pair(node->right ,level+1) );            q.pop();        }        //对于奇数行的数据翻转        for(int i = 1; i < res.size(); i+=2)            reverse(res[i].begin(), res[i].end());        return res;     }

leetcode 199

    vector<int> rightSideView(TreeNode* root) {        vector<int> res;        if(root == NULL)            return res;        //层序遍历        queue<pair<TreeNode*,int>> q;        //root作为第0层        q.push( make_pair(root,0) );        while(!q.empty()){            TreeNode* node = q.front().first;            int level = q.front().second;            //当level == res.size()时，说明res[level]为空，此时push            if(level == res.size()){                res.push_back(node->val);            }            //当level ！= res.size()时，说明res[level]已经存在，我们只需要将它覆盖，最后覆盖的值一定是该层最右边的值            else res[level] = (node->val);            if(node->left) q.push( make_pair(node->left ,level+1) );            if(node->right) q.push( make_pair(node->right ,level+1) );            q.pop();        }        return res;       }

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