算法描述:
Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it .
Example 1:
Input: [ [1,1,1], [1,0,1], [1,1,1]]Output: [ [1,0,1], [0,0,0], [1,0,1]]
Example 2:
Input: [ [0,1,2,0], [3,4,5,2], [1,3,1,5]]Output: [ [0,0,0,0], [0,4,5,0], [0,3,1,0]]
Follow up:
- 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?
解题思路:将矩阵的首行和首列用于标记该行或该列中有0元素。而首行和首列则需要单独的标记位标记该行或者列中有0元素存在。
void setZeroes(vector>& matrix) { int m = matrix.size(); int n = matrix[0].size(); bool row = false; bool col = false; for(int i=0; i < m; i++) if(matrix[i][0]==0) row = true; for(int j=0; j < n; j++) if(matrix[0][j]==0) col = true; for(int i=1; i < m; i++){ for(int j=1; j < n; j++){ if(matrix[i][j]==0){ matrix[i][0]=0; matrix[0][j]=0; } } } for(int i = 1; i < m; i++){ for(int j =1; j < n; j++){ if(matrix[i][0]==0 || matrix[0][j]==0){ matrix[i][j]=0; } } } if(row) for(int i=0; i < m; i++) matrix[i][0]=0; if(col) for(int i=0; i < n; i++) matrix[0][i]=0; }