Leetcode: Set Matrix Zeroes

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

click to show follow up.

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?

O(m+n）的方法比较容易想到，设置两个数组记录某行某列上是否出现过0即可。Constant space？驽钝啊，看了讨论区才知道。

class Solution {public:    void setZeroes(vector<vector<int> > &matrix) {        int rows = matrix.size();        if (rows == 0) return;        int cols = matrix[0].size();        if (cols == 0) return;                bool first_col_zero = false;        for (int i = 0; i < rows; ++i) {            if (matrix[i][0] == 0) {                first_col_zero = true;                break;            }        }                bool first_row_zero = false;        for (int j = 0; j < cols; ++j) {            if (matrix[0][j] == 0) {                first_row_zero = true;                break;            }        }                for (int i = 1; i < rows; ++i) {            for (int j = 1; j < cols; ++j) {                if (matrix[i][j] == 0) {                    matrix[i][0] = 0;                    matrix[0][j] = 0;                }            }        }                for (int i = 1; i < rows; ++i) {            for (int j = 1; j < cols; ++j) {                if (matrix[i][0] == 0 || matrix[0][j] == 0) {                    matrix[i][j] = 0;                }            }        }                if (first_col_zero) {            for (int i = 0; i < rows; ++i) {                matrix[i][0] = 0;            }        }        if (first_row_zero) {            for (int j = 0; j < cols; ++j) {                matrix[0][j] = 0;            }        }    }};

==============第二次================

稍微有点复杂了。

class Solution {public:    void setZeroes(vector<vector<int> > &matrix) {        if (matrix.empty() || matrix[0].empty()) {            return;        }                int rows = matrix.size();        int cols = matrix[0].size();        bool row_zero = false;        for (int i = 0; i < cols; ++i) {            if (matrix[0][i] == 0) {                row_zero = true;                break;            }        }        bool col_zero = false;        for (int i = 0; i < rows; ++i) {            if (matrix[i][0] == 0) {                col_zero = true;                break;            }        }                for (int i = 1; i < rows; ++i) {            for (int j = 1; j < cols; ++j) {                if (matrix[i][j] == 0) {                    matrix[i][0] = 0;                    matrix[0][j] = 0;                }            }        }                for (int j = 1; j < cols; ++j) {            if (matrix[0][j] == 0) {                for (int i = 1; i < rows; ++i) {                    matrix[i][j] = 0;                }            }        }        for (int i = 1; i < rows; ++i) {            if (matrix[i][0] == 0) {                for (int j = 1; j < cols; ++j) {                    matrix[i][j] = 0;                }            }        }        if (row_zero) {            for (int j = 0; j < cols; ++j) {                matrix[0][j] = 0;            }        }        if (col_zero) {            for (int i = 0; i < rows; ++i) {                matrix[i][0] = 0;            }        }    }};

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