Leetcode 73. Set Matrix Zeroes

题目

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?

思路

第一行以及第一列存储该行或者该列是否有０。扫描整个数组，得到第一行或者第一列。再扫描第一行以及第一列，将为０的行或者列全部设置为０

代码

package leetcodeArray;public class Leetcode73SetMatrixZeroes {    public void setZeroes(int[][] matrix) {        boolean fr = false, fc = false;        for(int i = 0; i < matrix.length; ++i){            for(int j = 0; j < matrix[0].length; ++j){                if(matrix[i][j] == 0){                    if(i == 0)      fr = true;                    if(j == 0)      fc = true;                    matrix[i][0] = 0;                    matrix[0][j] = 0;                }            }        }        for(int i = 1; i < matrix.length; ++i){            if(matrix[i][0] == 0){                for(int j = 1; j < matrix[0].length; ++j)                    matrix[i][j] = 0;            }        }        for(int j = 1; j < matrix[0].length; ++j){            if( matrix[0][j] == 0){                for(int i = 1; i < matrix.length; ++i)                    matrix[i][j] = 0;            }        }        if(fr) {            for(int j = 0; j < matrix[0].length; j++) {                matrix[0][j] = 0;            }        }        if(fc) {            for(int i = 0; i < matrix.length; i++) {                matrix[i][0] = 0;            }        }    }}

他山之玉

void setZeroes(vector<vector<int> > &matrix) {    int col0 = 1, rows = matrix.size(), cols = matrix[0].size();    for (int i = 0; i < rows; i++) {        if (matrix[i][0] == 0) col0 = 0;        for (int j = 1; j < cols; j++)            if (matrix[i][j] == 0)                matrix[i][0] = matrix[0][j] = 0;    }    for (int i = rows - 1; i >= 0; i--) {        for (int j = cols - 1; j >= 1; j--)            if (matrix[i][0] == 0 || matrix[0][j] == 0)                matrix[i][j] = 0;        if (col0 == 0) matrix[i][0] = 0;    }}