15. The K Weakest Rows in a Matrix.cpp

/*
The K Weakest Rows in a Matrix
==============================

Given a m * n matrix mat of ones (representing soldiers) and zeros (representing civilians), return the indexes of the k weakest rows in the matrix ordered from the weakest to the strongest.

A row i is weaker than row j, if the number of soldiers in row i is less than the number of soldiers in row j, or they have the same number of soldiers but i is less than j. Soldiers are always stand in the frontier of a row, that is, always ones may appear first and then zeros.

Example 1:
Input: mat = 
[[1,1,0,0,0],
 [1,1,1,1,0],
 [1,0,0,0,0],
 [1,1,0,0,0],
 [1,1,1,1,1]], 
k = 3
Output: [2,0,3]
Explanation: 
The number of soldiers for each row is: 
row 0 -> 2 
row 1 -> 4 
row 2 -> 1 
row 3 -> 2 
row 4 -> 5 
Rows ordered from the weakest to the strongest are [2,0,3,1,4]

Example 2:
Input: mat = 
[[1,0,0,0],
 [1,1,1,1],
 [1,0,0,0],
 [1,0,0,0]], 
k = 2
Output: [0,2]
Explanation: 
The number of soldiers for each row is: 
row 0 -> 1 
row 1 -> 4 
row 2 -> 1 
row 3 -> 1 
Rows ordered from the weakest to the strongest are [0,2,3,1]

Constraints:
m == mat.length
n == mat[i].length
2 <= n, m <= 100
1 <= k <= m
matrix[i][j] is either 0 or 1.

Hint #1  
Sort the matrix row indexes by the number of soldiers and then row indexes.
*/

class Solution
{
public:
  vector<int> kWeakestRows(vector<vector<int>> &mat, int k)
  {
    vector<vector<int>> count;
    for (int i = 0; i < mat.size(); ++i)
    {
      int sum = 0;
      for (int j = 0; j < mat[0].size(); ++j)
      {
        sum += mat[i][j];
      }
      count.push_back({sum, i});
    }
    sort(count.begin(), count.end());
    vector<int> ans;
    for (int i = 0; i < k; ++i)
      ans.push_back(count[i][1]);
    return ans;
  }
};