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import java.util.Arrays;

/**

* Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.

* <p/>

* Follow up:

* Did you use extra space?

* A straight forward 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?

*/

public class SetMatrixZero {

public static void main(String[] args) {

int[][] matrix = new int[][]{

{1, 2, 3, 5},

{2, 4, 0, 1},

{2, 4, 2, 1},

{0, 4, 2, 1},

};

System.out.println(Arrays.deepToString(matrix));

setMatrixZero(matrix);

System.out.println(Arrays.deepToString(matrix));

matrix = new int[][]{

{1, 2, 3, 5},

{2, 4, 0, 1},

{2, 4, 2, 1},

{0, 4, 2, 1},

};

setZeros(matrix);

System.out.println(Arrays.deepToString(matrix));

}

// do it in place

// use first row/col to record zero flag

public static void setMatrixZero(int[][] m) {

if (m.length <= 0) return;

int row = m.length;

int col = m[0].length;

boolean firstRowZero = false;

boolean firstColZero = false;

for (int j = 0; j < col; j++) {

if (m[0][j] == 0) {

firstRowZero = true;

break;

}

}

for (int i = 0; i < row; i++) {

if (m[i][0] == 0) {

firstColZero = true;

break;

}

}

for (int i = 1; i < row; i++) {

for (int j = 1; j < col; j++) {

if (m[i][j] == 0) {

// set zero flag on the first row/col

m[0][j] = 0;

m[i][0] = 0;

}

}

}

// set zero based on zero flag

for (int i = 1; i < row; i++) {

for (int j = 1; j < col; j++) {

if (m[0][j] == 0 || m[i][0] == 0) {

m[i][j] = 0;

}

}

}

if (firstRowZero) {

for (int j = 0; j < col; j++) {

m[0][j] = 0;

}

}

if (firstColZero) {

for (int i = 0; i < col; i++) {

m[i][0] = 0;

}

}

return;

}

// need extra space O(m+n)

public static void setZeros(int[][] matrix) {

boolean[] row = new boolean[matrix.length];

boolean[] column = new boolean[matrix[0].length];

// Store the row and column index with value 0

for (int i = 0; i < matrix.length; i++) {

for (int j = 0; j < matrix[0].length; j++) {

if (matrix[i][j] == 0) {

row[i] = true;

column[j] = true;

}

}

}

// Set arr[i][j] to 0 if either row i or column j has a 0

for (int i = 0; i < matrix.length; i++) {

for (int j = 0; j < matrix[0].length; j++) {

if (row[i] || column[j]) {

matrix[i][j] = 0;

}

}

}

}

}