Question
Given a boolean matrix, update it so that if any cell is true, all the cells in that row and column are true.
eg.
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[true, false, false] [true, true, true ] [false, false, false] -> [true, false, false] [false, false, false] [true, false, false] |
Once you think that you’ve solved the problem, click below to see the solution.
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Solution
How was that problem? You can check out the solution in the video below.
Here is the source code for the solution shown in the video (Github):
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public void zeroMatrix(boolean[][] matrix) { // Verify the input array is nonzero if (matrix.length == 0 || matrix[0].length == 0) return; // Determine whether the first row or first column is true boolean rowZero = false, colZero = false; for (boolean i : matrix[0]) { rowZero |= i; } for (boolean[] i : matrix) { colZero |= i[0]; } // For each cell not in the first row/column, if it is true, set the // cell in the first row/same column and first column/same row to be // true for (int i = 1; i < matrix.length; i++) { for (int j = 1; j < matrix[0].length; j++) { if (matrix[i][j]) { matrix[i][0] = true; matrix[0][j] = true; } } } // Go through the first column and set each row to true where cell in // the first column is true for (int i = 1; i < matrix.length; i++) { if (matrix[i][0]) { for (int j = 1; j < matrix[i].length; j++) { matrix[i][j] = true; } } } // Repeat for the rows for (int j = 1; j < matrix[0].length; j++) { if (matrix[0][j]) { for (int i = 1; i < matrix.length; i++) { matrix[i][j] = true; } } } // Set first row/column to true if necessary if (rowZero) { for (int i = 0; i < matrix[0].length; i++) { matrix[0][i] = true; } } if (colZero) { for (int i = 0; i < matrix.length; i++) { matrix[i][0] = true; } } } |
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