73.java

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sample 0 ms submission
class Solution {
    public void setZeroes(int[][] matrix) {
        if (matrix == null || matrix.length == 0) {
            return;
        }
        int m = matrix.length;
        int n = matrix[0].length;
        if (n == 0) {
            return;
        }
        boolean firstColZero = false;
        for (int i = 0; i < m; i++) {
            if (matrix[i][0] == 0) {
                firstColZero = true;
            }
            for (int j = 1; j < n; j++) {
                if (matrix[i][j] == 0) {
                    matrix[i][0] = 0;
                    matrix[0][j] = 0;
                }
            }
        }
        for (int i = 1; i < m; i++) {
            for (int j = 1; j < n; j++) {
                if (matrix[i][0] == 0 || matrix[0][j] == 0) {
                    matrix[i][j] = 0;
                }
            }
        }
        if (matrix[0][0] == 0) {
            for (int j = 0; j < n; j++) {
                matrix[0][j] = 0;
            } 
        }
        if (firstColZero) {
            for (int i = 0; i < m; i++) {
                matrix[i][0] = 0;
            }
        }
        return;
    }
}
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sample 38228 kb submission
class Solution {
  public void setZeroes(int[][] matrix) {
    int R = matrix.length;
    int C = matrix[0].length;
    Set<Integer> rows = new HashSet<Integer>();
    Set<Integer> cols = new HashSet<Integer>();

    // Essentially, we mark the rows and columns that are to be made zero
    for (int i = 0; i < R; i++) {
      for (int j = 0; j < C; j++) {
        if (matrix[i][j] == 0) {
          rows.add(i);
          cols.add(j);
        }
      }
    }

    // Iterate over the array once again and using the rows and cols sets, update the elements.
    for (int i = 0; i < R; i++) {
      for (int j = 0; j < C; j++) {
        if (rows.contains(i) || cols.contains(j)) {
          matrix[i][j] = 0;
        }
      }
    }
  }
}
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