Binary Tree Vertical Order Traversal

Data Structure to catch the nodes

map<int, map<int, vector<int>>

1) The first int indicates the index or columns;

2) The second int indicates the index of rows;

3) The vector<int> indicates what's inside that column and that row;

code

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> verticalOrder(TreeNode* root) {
        vector<vector<int>> ret;
        if(root == NULL)
        {
            return ret;
        }

        map<int, map<int, vector<int>>> hash;
        traversal(root, hash, 0, 0);

        for(auto& kv : hash)
        {
            vector<int> tmp;
            for(auto& kv2 : kv.second)
            {
                for(int i : kv2.second)
                {
                    tmp.push_back(i);
                }
            }
            ret.push_back(tmp);
        }

        return ret;
    }

    void traversal(TreeNode* root, map<int, map<int, vector<int>>>& hash, int index, int level)
    {
        if(root == NULL)
        {
            return ;
        }

        hash[index][level].push_back(root->val);
        traversal(root->left, hash, index-1, level+1);
        traversal(root->right, hash, index+1, level+1);
    }
};