LC 987. Vertical Order Traversal of a Binary Tree

发布时间：2020-12-14 04:26:04 所属栏目：大数据来源：网络整理

导读：Given a binary tree,return the? vertical order ?traversal of its nodes?values. For each node at position? (X,Y) ,its left and right children respectively?will be at positions? (X-1,Y-1) ?and? (X+1,Y-1) . Running a vertical line from? X = -

Given a binary tree,return the?vertical order?traversal of its nodes?values.

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

Running a vertical line from?X = -infinity?to?X = +infinity,whenever the vertical line touches some nodes,we report the values of the nodes in order from top to bottom (decreasing?Y?coordinates).

If two nodes have the same position,then the value of the node that is reported first is the value that is smaller.

Return an list?of non-empty reports in order of?X?coordinate.? Every report will have a list of values of nodes.

class Solution {
public:
  vector<vector<int>> verticalTraversal(TreeNode* root) {
    map<int,map<int,vector<int>>> mp;
    vector<vector<int>> ret;
    helper(root,0,0,mp);
    for(auto it=mp.begin(); it!=mp.end(); it++){
      vector<int> a;
      for(auto iit=it->second.rbegin(); iit!=it->second.rend(); iit++) {
        vector<int> tmp = iit->second;
        sort(tmp.begin(),tmp.end());
        for(auto x : tmp) a.push_back(x);
      }
      ret.push_back(a);
    }
    return ret;
  }
  void helper(TreeNode* root,int x,int y,vector<int>>>& mp){
    if(!root) return;
    mp[x][y].push_back(root->val);
    helper(root->left,x-1,y-1,mp);
    helper(root->right,x+1,mp);
  }
};

（编辑：李大同）

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