[leetcode] day94 reshape matrix

subject

566. Reshaping the matrix 【 Simple 】

Answer key

One dimensional representation of a two-dimensional array

What the topic requires us to do is equivalent to ：

• Put two-dimensional array nums Map to a one-dimensional array ;
• Map this one-dimensional array back to r That's ok c Two dimensional array of columns .

The principle is ： about x∈[0,mn), The first x The elements are nums The corresponding subscript in is (x / n,x % n), In the new remodeling matrix, the corresponding subscript is (x / c,x % c). So we can make corresponding mapping in the code .

class Solution {
    
    public int[][] matrixReshape(int[][] mat, int r, int c) {
    
        int m=mat.length,n=mat[0].length;
        if(m*n!=r*c)
            return mat;
        
        int[][] newMat=new int[r][c];
        for(int num=0;num<m*n;num++){
    
            newMat[num/c][num%c]=mat[num/n][num%n];
        }
        return newMat;
    }
}

Time complexity ：$O(rc)$

Spatial complexity ：$O(1)$