```
public int[][] matrixReshape(int[][] nums, int r, int c) {
int n = nums.length, m = nums[0].length;
if (r*c != n*m) return nums;
int[][] res = new int[r][c];
for (int i=0;i<r*c;i++)
res[i/c][i%c] = nums[i/m][i%m];
return res;
}
```