矩阵置零

1、题目

图一

2、题解

两次扫matrix

第一遍记录数组中0的坐标，第二遍置零

class Solution:
    def setZeroes(self, matrix: List[List[int]]) -> None:
        """
        Do not return anything, modify matrix in-place instead.
        """
        lines = []
        rows = []
        for i in range(len(matrix)):
            for j in range(len(matrix[0])):
                if matrix[i][j] == 0:
                    lines.append(j)
                    rows.append(i)
 
        for h in range(len(matrix)):
            for line in lines:
                matrix[h][line] = 0

        for row in rows:
            matrix[row] = [0]*len(matrix[0])
                

用O(1)空间

class Solution:
    def setZeroes(self, matrix: List[List[int]]) -> None:
        """
        Do not return anything, modify matrix in-place instead.
        """
        flag_col = False
        row = len(matrix)
        col = len(matrix[0])
        for i in range(row):
            if matrix[i][0] == 0: flag_col = True
            for j in range(1,col):
                if matrix[i][j] == 0:
                    matrix[i][0] = matrix[0][j] = 0
        
        for i in range(row - 1, -1, -1):
            for j in range(col - 1, 0, -1):
                if matrix[i][0] == 0 or matrix[0][j] == 0:
                    matrix[i][j] = 0

            if flag_col == True: matrix[i][0] = 0