[LeetCode] Set Matrix Zeros

最新推荐文章于 2024-08-16 09:55:14 发布

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本文提供了一种高效的算法来解决给定矩阵中若存在0则将其所在行和列全部置为0的问题，并实现了常数空间复杂度的解决方案。

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[Problem]

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

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?

[Solution]

class Solution {
public:
    void setZeroes(vector<vector<int> > &matrix) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
       
        // get m
        int m = matrix.size();
        if(m <= 0){
            return;
        }
       
        // get n
        int n = matrix[0].size();
       
        // find rows and columns contain 0
        bool row0 = false, column0 = false;
        for(int i = 0; i < m; ++i){
            for(int j = 0; j < n; ++j){
                if(matrix[i][j] == 0){
                    matrix[0][j] = 0;
                    matrix[i][0] = 0;
                    if(i == 0){
                        row0 = true;
                    }
                    if(j == 0){
                        column0 = true;
                    }
                }
            }
        }
       
        // set 0 columns
        for(int i = 1; i < n; ++i){
            if(matrix[0][i] == 0){
                for(int j = 1; j < m; ++j){
                    matrix[j][i] = 0;
                }
            }
        }
       
        // set 0 rows
        for(int i = 1; i < m; ++i){
            if(matrix[i][0] == 0){
                for(int j = 1; j < n; ++j){
                    matrix[i][j] = 0;
                }
            }
        }
       
        // set row0 and column0
        if(row0){
            for(int i = 0; i < n; ++i){
                matrix[0][i] = 0;
            }
        }
        if(column0){
            for(int i = 0; i < m; ++i){
                matrix[i][0] = 0;
            }
        }
    }
};