508. Most Frequent Subtree Sum

Given the root of a tree, you are asked to find the most frequent
subtree sum. The subtree sum of a node is defined as the sum of all
the node values formed by the subtree rooted at that node (including
the node itself). So what is the most frequent subtree sum value? If
there is a tie, return all the values with the highest frequency in
any order.

• Examples 1 Input:

  5 / \ 2 -3 return [2, -3, 4], since all the values happen only
  once, return all of them in any order.

• Examples 2 Input:

  5 / \ 2 -5 return [2], since 2 happens twice, however -5 only
  occur once. Note: You may assume the sum of values in any subtree is
  in the range of 32-bit signed integer.

/** * Def * 列表内容inition 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:    int Dfs(TreeNode *root,vector<int> & sumVec) {        if(root == NULL){            return 0;        }        int l = Dfs(root->left,sumVec);        int r = Dfs(root->right,sumVec);        int sum = l + r + root->val;        sumVec.push_back(sum);        return sum;    }    vector<int> findFrequentTreeSum(TreeNode* root) {        vector<int> sumVec;        vector<int> result;        map<int,int> sumMap;        int max = -1;        if(root == NULL){            return result;        }        Dfs(root,sumVec);        for(int i = 0; i<sumVec.size(); i++)         {             map<int,int>::iterator key = sumMap.find(sumVec[i]);            if(key == sumMap.end()){                sumMap.insert(make_pair(sumVec[i],1));             }else{                key->second = key->second + 1;            }                  }         map<int,int>::iterator myItr = sumMap.begin();        for(;myItr!=sumMap.end();myItr++){            if(myItr->second > max){                max = myItr->second;            }        }        myItr = sumMap.begin();        for(;myItr!=sumMap.end();myItr++){            if(myItr->second == max){                result.push_back(myItr->first);            }        }        return result;    }};