LeetCode-in-All

73. Set Matrix Zeroes

Medium

Given an m x n integer matrix matrix, if an element is 0, set its entire row and column to 0’s.

You must do it in place.

Example 1:

Input: matrix = [[1,1,1],[1,0,1],[1,1,1]]

Output: [[1,0,1],[0,0,0],[1,0,1]]

Example 2:

Input: matrix = [[0,1,2,0],[3,4,5,2],[1,3,1,5]]

Output: [[0,0,0,0],[0,4,5,0],[0,3,1,0]]

Constraints:

• m == matrix.length
• n == matrix[0].length
• 1 <= m, n <= 200
• -231 <= matrix[i][j] <= 231 - 1

Follow up:

• A straightforward solution using O(mn) space is probably a bad idea.
• A simple improvement uses O(m + n) space, but still not the best solution.
• Could you devise a constant space solution?

Solution

class Solution {
  void setZeroes(List<List<int>> matrix) {
    int nRow = matrix.length;
    int nCol = matrix.first.length;
    bool fr = false;
    bool lr = false;
    bool fc = false;
    bool lc = false;

    for (int i = 0; i < nCol; i++) {
      if (matrix[0][i] == 0) {
        fr = true;
      }
      if (matrix[nRow - 1][i] == 0) {
        lr = true;
      }
    }

    for (int i = 0; i < nRow; i++) {
      if (matrix[i][0] == 0) {
        fc = true;
      }
      if (matrix[i][nCol - 1] == 0) {
        lc = true;
      }
    }

    for (int i = 1; i < nRow - 1; i++) {
      for (int j = 1; j < nCol - 1; j++) {
        if (matrix[i][j] == 0) {
          matrix[0][j] = 0;
          matrix[i][0] = 0;
        }
      }
    }

    for (int i = 1; i < nRow - 1; i++) {
      if (matrix[i][0] == 0 || matrix[i][nCol - 1] == 0) {
        for (int j = 0; j < nCol; j++) {
          matrix[i][j] = 0;
        }
      }
    }

    for (int i = 1; i < nCol - 1; i++) {
      if (matrix[0][i] == 0 || matrix[nRow - 1][i] == 0) {
        for (int j = 0; j < nRow; j++) {
          matrix[j][i] = 0;
        }
      }
    }


    if (fr) {
      for (int i = 0; i < nCol; i++) {
        matrix[0][i] = 0;
      }
    }
    if (lr) {
      for (int i = 0; i < nCol; i++) {
        matrix[nRow - 1][i] = 0;
      }
    }
    if (fc) {
      for (int i = 0; i < nRow; i++) {
        matrix[i][0] = 0;
      }
    }
    if (lc) {
      for (int i = 0; i < nRow; i++) {
        matrix[i][nCol - 1] = 0;
      }
    }
  }
}

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