566. Reshape the Matrix

问题概述
In MATLAB, there is a handy function called reshape which can reshape an m x n matrix into a new one with a different size r x c keeping its original data.

You are given an m x n matrix mat and two integers r and c representing the number of rows and the number of columns of the wanted reshaped matrix.

The reshaped matrix should be filled with all the elements of the original matrix in the same row-traversing order as they were.

If the reshape operation with given parameters is possible and legal, output the new reshaped matrix; Otherwise, output the original matrix.

根据数组的数学公式得出其位置，一次遍历将原数组中的数字填入。
O(r*c)

class Solution {
    public int[][] matrixReshape(int[][] mat, int r, int c) {
        
        int[][] ans = new int[r][c];

        int oldR = mat.length;
        int oldC = mat[0].length;
        
        
        if ( oldR * oldC != r * c ){
            return mat;
        }
        for (int i = 0; i < r*c ; i++ ){
            int m = i/oldC;
            int n = i%oldC;
            
            int p = i/c;
            int q = i%c;        
            ans[p][q] = mat[m][n];
        }
        return ans;
    }
}