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

July LeetCoding Challenge 20

Description

Find Valid Matrix Given Row and Column Sums

You are given two arrays rowSum and colSum of non-negative integers where rowSum[i] is the sum of the elements in the ith row and colSum[j] is the sum of the elements of the jth column of a 2D matrix. In other words, you do not know the elements of the matrix, but you do know the sums of each row and column.

Find any matrix of non-negative integers of size rowSum.length x colSum.length that satisfies the rowSum and colSum requirements.

Return a 2D array representing any matrix that fulfills the requirements. It's guaranteed that at least one matrix that fulfills the requirements exists.

Example 1:

Input: rowSum = [3,8], colSum = [4,7]
Output: [[3,0],
         [1,7]]
Explanation: 
0th row: 3 + 0 = 3 == rowSum[0]
1st row: 1 + 7 = 8 == rowSum[1]
0th column: 3 + 1 = 4 == colSum[0]
1st column: 0 + 7 = 7 == colSum[1]
The row and column sums match, and all matrix elements are non-negative.
Another possible matrix is: [[1,2],
                             [3,5]]

Example 2:

Input: rowSum = [5,7,10], colSum = [8,6,8]
Output: [[0,5,0],
         [6,1,0],
         [2,0,8]]

Constraints:

• 1 <= rowSum.length, colSum.length <= 500
• 0 <= rowSum[i], colSum[i] <= 108
• sum(rowSum) == sum(colSum)

Solution

class Solution {
public:
  vector<vector<int>> restoreMatrix(vector<int>& rowSum, vector<int>& colSum) {
    int rows = rowSum.size();
    int cols = colSum.size();
    int curRow = 0;
    int curCol = 0;
    vector<vector<int>> answer(rows, vector<int>(cols, 0));

    while(curRow < rows || curCol < cols) {
      if(curRow >= rows) {
        answer[rows  - 1][curCol] = colSum[curCol];
        curCol += 1;
        continue;
      } else if(curCol >= cols) {
        answer[curRow][cols - 1] = rowSum[curRow];
        curRow += 1;
        continue;
      }

      int value = min(rowSum[curRow], colSum[curCol]);
      rowSum[curRow] -= value;
      colSum[curCol] -= value;
      answer[curRow][curCol] = value;

      if(!rowSum[curRow]) {
        curRow += 1;
      }
      if(!colSum[curCol]) {
        curCol += 1;
      }
    }

    return answer;
  }
};