LEETCODE算法:199. Binary Tree Right Side View

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题目

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.

Example:

Input: [1,2,3,null,5,null,4] Output: [1, 3, 4] Explanation:

1 <--- /
2 3 <---  
5 4 <---

题解

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
//层次遍历（广搜），每层最后一个是右视图
class Solution {
public:
    vector<int> rightSideView(TreeNode* root) {
        vector<int> ans;
        if(root==NULL) return ans;
        queue<pair<TreeNode*,int>> q;
        q.push({root,0});
        int pre=root->val,prei=0;
        while(!q.empty())
        {
            auto [tmp,i]=q.front();//指针，当前层数
            if(i>prei)
            {
                ans.push_back(pre);
                prei=i;
            }
            pre=tmp->val;
            q.pop();
            if(tmp->left!=NULL) q.push({tmp->left,i+1});
            if(tmp->right!=NULL) q.push({tmp->right,i+1});
        }
        ans.push_back(pre);
        return ans;
    }
};
  • 也可以深度优先搜索，先有右后左每层第一个为右视图，先左后右每层最后一个是右视图元素