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LeetCode 987. Vertical Order Traversal of a Binary Tree

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题目

原题在此

Given the root of a binary tree, calculate the vertical order traversal of the binary tree.

For each node at position (x, y), its left and right children will be at positions (x - 1, y - 1) and (x + 1, y - 1) respectively.

The vertical order traversal of a binary tree is a list of non-empty reports for each unique x-coordinate from left to right. Each report is a list of all nodes at a given x-coordinate. The report should be primarily sorted by y-coordinate from highest y-coordinate to lowest. If any two nodes have the same y-coordinate in the report, the node with the smaller value should appear earlier.

Return the vertical order traversal of the binary tree.

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: [[9],[3,15],[20],[7]]

Explanation: Without loss of generality, we can assume the root node is at position (0, 0):
The node with value 9 occurs at position (-1, -1).
The nodes with values 3 and 15 occur at positions (0, 0) and (0, -2).
The node with value 20 occurs at position (1, -1).
The node with value 7 occurs at position (2, -2).

Example 2:

Input: root = [1,2,3,4,5,6,7]
Output: [[4],[2],[1,5,6],[3],[7]]

Explanation: The node with value 5 and the node with value 6 have the same position according to the given scheme.
However, in the report [1,5,6], the node with value 5 comes first since 5 is smaller than 6.

Constraints:

  • The number of nodes in the tree is in the range [1, 1000].
  • 0 <= Node.val <= 1000

解析

代码

c++

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:    
    struct Foo {
        TreeNode* node;
        int x;
        int y;
    };
    vector<vector<int>> verticalTraversal(TreeNode* root) {
        map<int, map<int, multiset<int>>> mp;
        queue<Foo> q;
        q.push({root, 0, 0});
        while (!q.empty()) {
            Foo tmp = q.front();
            q.pop();
            if(tmp.node -> left ) {q.push({tmp.node -> left , tmp.x - 1, tmp.y - 1});}
            if(tmp.node -> right) {q.push({tmp.node -> right, tmp.x + 1, tmp.y - 1});}
            mp[tmp.x][tmp.y].insert(tmp.node -> val);
        }
        vector<vector<int>> res;
        for (auto & [key, val] : mp) {
            vector<int> tmp;
            for (auto & [nonUsed, set] : val) {
                tmp.insert(tmp.begin(), set.begin(), set.end());
            }
            res.push_back(tmp);
        }
        return res;
    }
};