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

July LeetCoding Challenge 21

Description

Build a Matrix With Conditions

You are given a positive integer k. You are also given:

• a 2D integer array rowConditions of size n where rowConditions[i] = [abovei, belowi], and
• a 2D integer array colConditions of size m where colConditions[i] = [lefti, righti].

The two arrays contain integers from 1 to k.

You have to build a k x k matrix that contains each of the numbers from 1 to k exactly once. The remaining cells should have the value 0.

The matrix should also satisfy the following conditions:

• The number abovei should appear in a row that is strictly above the row at which the number belowi appears for all i from 0 to n - 1.
• The number lefti should appear in a column that is strictly left of the column at which the number righti appears for all i from 0 to m - 1.

Return any matrix that satisfies the conditions. If no answer exists, return an empty matrix.

Example 1:

Input: k = 3, rowConditions = [[1,2],[3,2]], colConditions = [[2,1],[3,2]]
Output: [[3,0,0],[0,0,1],[0,2,0]]
Explanation: The diagram above shows a valid example of a matrix that satisfies all the conditions.
The row conditions are the following:
- Number 1 is in row 1, and number 2 is in row 2, so 1 is above 2 in the matrix.
- Number 3 is in row 0, and number 2 is in row 2, so 3 is above 2 in the matrix.
The column conditions are the following:
- Number 2 is in column 1, and number 1 is in column 2, so 2 is left of 1 in the matrix.
- Number 3 is in column 0, and number 2 is in column 1, so 3 is left of 2 in the matrix.
Note that there may be multiple correct answers.

Example 2:

Input: k = 3, rowConditions = [[1,2],[2,3],[3,1],[2,3]], colConditions = [[2,1]]
Output: []
Explanation: From the first two conditions, 3 has to be below 1 but the third conditions needs 3 to be above 1 to be satisfied.
No matrix can satisfy all the conditions, so we return the empty matrix.

Constraints:

• 2 <= k <= 400
• 1 <= rowConditions.length, colConditions.length <= 104
• rowConditions[i].length == colConditions[i].length == 2
• 1 <= abovei, belowi, lefti, righti <= k
• abovei != belowi
• lefti != righti

Solution

class Solution {
  vector<int> sort(int k, const vector<vector<int>>& conditions) {
    vector<int> degree(k + 1);
    vector<vector<int>> neighbor(k + 1);
    for(const auto &con : conditions) {
      degree[con[1]] += 1;
      neighbor[con[0]].push_back(con[1]);
    }

    queue<int> q;
    for(int i = 1; i <= k; ++i) {
      if(!degree[i]) q.push(i);
    }
    vector<int> result;
    while(q.size()) {
      auto current = q.front();
      q.pop();
      result.push_back(current);
      for(auto next : neighbor[current]) {
        degree[next] -= 1;
        if(!degree[next]) q.push(next);
      }
    }

    return result.size() == k ? result : vector<int>();
  }
public:
  vector<vector<int>> buildMatrix(int k, vector<vector<int>>& rowConditions, vector<vector<int>>& colConditions) {
    auto rows = sort(k, rowConditions);
    auto cols = sort(k, colConditions);

    if(rows.empty() || cols.empty()) return {};

    vector<vector<int>> answer(k, vector<int>(k));
    vector<int> posRow(k + 1);
    vector<int> posCol(k + 1);
    for(int i = 0; i < k; ++i) {
      posRow[rows[i]] = i;
      posCol[cols[i]] = i;
    }
    for(int i = 1; i <= k; ++i) {
      answer[posRow[i]][posCol[i]] = i;
    }

    return answer;
  }
};