[LeetCode] Set Matrix Zeroes

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

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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?

 

思路：主要考察的是空间复杂度，

方法一：用rowHasZero记录这一行是否有0 存在，用colHaszero记录这一列是否有0存在。后面处理rowHasZero和colHaszero。空间复杂度O（m+n）

class Solution {
    public:
        void setZeroes(vector<vector<int> > &matrix)
        {   
            size_t row = matrix.size();
            if(row == 0)
                return;
            size_t col = matrix[0].size();

            vector<bool> rowHasZero(row, false); 
            vector<bool> colHasZero(col, false); 

            for(int i = 0; i < row; i++)
            {   
                for(int j = 0; j < col; j++)
                {   
                    if(matrix[i][j] == 0)
                    {   
                        rowHasZero[i] = true;
                        colHasZero[j] = true;
                    }   
                }   
            }   

            for(int i = 0; i < row; i++)
            {   
                if(rowHasZero[i])
                {   
                    for(int j = 0; j < col; j++)
                    {   
                        matrix[i][j] = 0;
                    }   
                }   
            }   
            for(int i = 0; i < col; i++)
            {
                if(colHasZero[i])
                {
                    for(int j = 0; j < row; j++)
                    {
                        matrix[j][i] = 0;
                    }
                }
            }
        }
};

 方法二：空间复杂度O（1），用第0行记录列是否有0，用第0列记录行是否有0，先判断行0和列0是否有0，然后处理矩阵，若matrix[i][j]为0，设置matrix[i][0] = 0; matrix[0][j] = 0;，然后根据matrix[i][0]和matrix[0][j]来设置设置相应的行、列为0，最后处理行0，列0.

class Solution {
    public:
        void setZeroes(vector<vector<int> > &matrix)
        {
            size_t row = matrix.size();
            if(row == 0)
                return;
            size_t col = matrix[0].size();

            bool rowZeroHasZero = false;
            bool colZeroHasZero = false;

            for(int i = 0; i < col; i++)
            {
                if(matrix[0][i] == 0)
                {
                    rowZeroHasZero = true;
                    break;
                }
            }
            for(int i = 0; i < row; i++)
            {
                if(matrix[i][0] == 0)
                {
                    colZeroHasZero = true;
                    break;
                }
            }

            //cout << rowZeroHasZero << endl;
            //cout << colZeroHasZero << endl;

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

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

            //handle the first row & first col
            if(rowZeroHasZero)
            {
                for(int j = 0; j < col; j++)
                {
                    matrix[0][j] = 0;
                }

            }
            if(colZeroHasZero)
            {
                for(int i = 0; i < row; i++)
                {
                    matrix[i][0] = 0;
                }

            }
        }
};