Today I have done leetcode's January LeetCoding Challenge with cpp.

January LeetCoding Challenge 12

Description

Number of Nodes in the Sub-Tree With the Same Label

You are given a tree (i.e. a connected, undirected graph that has no cycles) consisting of n nodes numbered from 0 to n - 1 and exactly n - 1 edges. The root of the tree is the node 0, and each node of the tree has a label which is a lower-case character given in the string labels (i.e. The node with the number i has the label labels[i]).

The edges array is given on the form edges[i] = [ai, bi], which means there is an edge between nodes ai and bi in the tree.

Return an array of size n where ans[i] is the number of nodes in the subtree of the ith node which have the same label as node i.

A subtree of a tree T is the tree consisting of a node in T and all of its descendant nodes.

Example 1:

Input: n = 7, edges = [[0,1],[0,2],[1,4],[1,5],[2,3],[2,6]], labels = "abaedcd"
Output: [2,1,1,1,1,1,1]
Explanation: Node 0 has label 'a' and its sub-tree has node 2 with label 'a' as well, thus the answer is 2. Notice that any node is part of its sub-tree.
Node 1 has a label 'b'. The sub-tree of node 1 contains nodes 1,4 and 5, as nodes 4 and 5 have different labels than node 1, the answer is just 1 (the node itself).

Example 2:

Input: n = 4, edges = [[0,1],[1,2],[0,3]], labels = "bbbb"
Output: [4,2,1,1]
Explanation: The sub-tree of node 2 contains only node 2, so the answer is 1.
The sub-tree of node 3 contains only node 3, so the answer is 1.
The sub-tree of node 1 contains nodes 1 and 2, both have label 'b', thus the answer is 2.
The sub-tree of node 0 contains nodes 0, 1, 2 and 3, all with label 'b', thus the answer is 4.

Example 3:

Input: n = 5, edges = [[0,1],[0,2],[1,3],[0,4]], labels = "aabab"
Output: [3,2,1,1,1]

Constraints:

• 1 <= n <= 105
• edges.length == n - 1
• edges[i].length == 2
• 0 <= ai, bi < n
• ai != bi
• labels.length == n
• labels is consisting of only of lowercase English letters.

Solution

class Solution {
  vector<vector<int>> count;
  vector<vector<int>> neighbors;
  void dfs(int current, int parrent, vector<int> &answer, string &labels) {
    for(auto next : neighbors[current]) {
      if(parrent == next) continue;
      dfs(next, current, answer, labels);
      for(int i = 0; i < 26; ++i) {
        count[i][current] += count[i][next];
      }
    }
    count[labels[current] - 'a'][current] += 1;
    answer[current] = count[labels[current] - 'a'][current];
  }
public:
  vector<int> countSubTrees(int n, vector<vector<int>>& edges, string labels) {
    neighbors.resize(n);
    count.resize(26, vector<int>(n));
    for(const auto &edge : edges) {
      neighbors[edge[0]].push_back(edge[1]);
      neighbors[edge[1]].push_back(edge[0]);
    }

    vector<int> answer(n);
    dfs(0, -1, answer, labels);

    return answer;
  }
};

// Accepted
// 59/59 cases passed (595 ms)
// Your runtime beats 82.96 % of cpp submissions
// Your memory usage beats 82.22 % of cpp submissions (181.6 MB)