[LeetCode] Binary Tree Right Side View，leetcodebinary

[LeetCode] Binary Tree Right Side View，leetcodebinary

Binary Tree Right Side View

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

For example:
Given the following binary tree,

   1            <--- /   \2     3         <--- \     \  5     4       <---

You should return [1, 3, 4].

解題思路：這道題較為簡單，可以用類似於先序遍曆的辦法來做，但是有點不同，遍曆的順序是根，右，左。用一個map記錄每一層第一個出現的值。下面是代碼：

/** * 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> rightSideView(TreeNode *root) {        map<int, int> levelToVal;   //記錄每一層第一個出現的數值。        tranver(root, 0, levelToVal);                vector<int> result;                for(map<int, int>::iterator it=levelToVal.begin(); it!=levelToVal.end(); it++){            result.push_back(it->second);        }                return result;    }        //類似於先序遍曆，但是，順序是上，右，左    void tranver(TreeNode* node, int level, map<int, int>& levelToVal){        if(node==NULL){            return;        }        map<int, int>::iterator it=levelToVal.find(level);        if(it==levelToVal.end()){            levelToVal.insert(map<int, int>::value_type(level, node->val));        }        tranver(node->right, level+1, levelToVal);        tranver(node->left, level+1, levelToVal);    }};