cci-Q1.7 二維數組置0

原文：

Write an algorithm such that if an element in an MxN matrix is 0, its entire row and column is set to 0.

譯文：

寫一個函數處理一個MxN的矩陣，如果矩陣中某個元素為0，那麼把它所在的行和列都置為0.

不能直接進行周遊置0，因為在周遊的過程中可能遇到之前被置0的元素而不是矩陣元素本身。首先進行周遊，記錄下存在0的行和列，然後根據記錄的數組重新周遊矩形進行置0操作。

public static int[][] setZero(int[][] matrix) {
        if (matrix == null) {
            return null;
        }

        int row = matrix.length;
        int column = 0;
        if (row > 0) {
            column = matrix[0].length;
        }

        int[] rows = new int[row];
        int[] columns = new int[column];

        for (int i = 0; i < row; i++) {
            for (int j = 0; j < column; j++) {
                if (0 == matrix[i][j]) {
                    rows[i] = 1;
                    columns[j] = 1;
                }
            }
        }

        for (int i = 0; i < row; i++) {
            for (int j = 0; j < column; j++) {
                if (1 == rows[i] || 1 == columns[j]) {
                    matrix[i][j] = 0;
                }
            }
        }

        return matrix;
    }
           

junit testcase

@Test
    public void testSetZero() {
        System.out.println("setZero");
        int[][] test = null;
        int[][] expected = null;
        assertArrayEquals(expected, q1_7.setZero(test));
        int[][] test1 = {};
        int[][] expected1 = {};
        assertArrayEquals(expected1, q1_7.setZero(test1));
        int[][] test2 = {{1, 1, 1}, {1, 0, 1}, {1, 1, 1}};
        int[][] expected2 = {{1, 0, 1}, {0, 0, 0}, {1, 0, 1}};
        assertArrayEquals(expected2, q1_7.setZero(test2));
        int[][] test3 = {{1, 0, 1, 1, 1}, {1, 1, 1, 0, 1}, {1, 1, 1, 1, 1}};
        int[][] expected3 = {{0, 0, 0, 0, 0}, {0, 0, 0, 0, 0}, {1, 0, 1, 0, 1}};
        assertArrayEquals(expected3, q1_7.setZero(test3));
    }