LeetCode 73. Matrix zeroing (java implementation)

73. Matrix zeroing

Given an mxn matrix, if an element is 0 , set all elements in its row and column to 0. Please use the in-place algorithm.

Example 1:

输入：matrix = [[1,1,1],[1,0,1],[1,1,1]]
输出：[[1,0,1],[0,0,0],[1,0,1]]

Example 2:

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

hint:

• m == matrix.length
• n == matrix[0].length
• 1 <= m, n <= 200
• -2^31 <= matrix[i][j] <= 2^31 - 1

Answer ideas:

• Scan the elements of the two-dimensional array. If the scanned element is 0, record the row and set all rows to 0.
• And use a column array to count which column should be set to 0
• Finally, scan the column array and set the columns that need to be set to 0.

class Solution {
    
    
    // 原地换0 数字范围是int的范围
    public void setZeroes(int[][] matrix) {
    
    
        int[] n = new int[matrix[0].length]; // TODO 额外的空间
        for (int i = 0; i < matrix.length; i++) {
    
    
            for (int j = 0; j < matrix[i].length; j++) {
    
    
                if (matrix[i][j] == 0) {
    
    
                    matrix[i][0] = 0; // TODO 将当前行标记为已置为1
                    n[j] = 1; // TODO 将当列标记为已置为1
                }
            }
            if (matrix[i][0] == 0) {
    
    
                int index = 0;
                while (index < matrix[i].length) {
    
     // 先把统计 后把行替换为0 避免替换覆盖掉其他覆盖掉其他的列的替换细节
                    matrix[i][index++] = 0;
                }
            }
        }
        for (int i = 0; i < n.length; i++) {
    
    
            if (n[i] == 1) {
    
    
                int index = 0;
                while (index < matrix.length) {
    
     // 最后列替换为0
                    matrix[index++][i] = 0;
                }
            }
        }
    }
}