leetcode566. Reshape the Matrix

566. Reshape the Matrix

In MATLAB, there is a very useful function called ‘reshape’, which can reshape a matrix into a new one with different size but keep its original data.

You’re given a matrix represented by a two-dimensional array, and two positive integers r and c representing the row number and column number of the wanted reshaped matrix, respectively.

The reshaped matrix need to 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.

Example 1:Input: nums = [[1,2], [3,4]]r = 1, c = 4Output: [[1,2,3,4]]Explanation:The row-traversing of nums is [1,2,3,4]. The new reshaped matrix is a 1 * 4 matrix, fill it row by row by using the previous list.Example 2:Input: nums = [[1,2], [3,4]]r = 2, c = 4Output: [[1,2], [3,4]]

Explanation:
There is no way to reshape a 2 * 2 matrix to a 2 * 4 matrix. So output the original matrix.
Note:
The height and width of the given matrix is in range [1, 100].
The given r and c are all positive.

解法

第几个元素 / 列数 是 所在的行数，% 列数 是 所在的列数。

public class Solution {    public int[][] matrixReshape(int[][] nums, int r, int c) {        if (nums == null || nums.length == 0) {            return null;        }        if (nums[0] == null || nums[0].length == 0) {            return null;        }        int x = nums.length;        int y = nums[0].length;        int len = x * y;        if (len != r * c) {            return nums;        }        int[][] reshape = new int[r][c];        for (int i = 0; i < r; i++) {            for (int j = 0; j < c; j++) {                int temp = i * c + j;                int position_x = temp / y;                int position_y = temp % y;                reshape[i][j] = nums[position_x][position_y];            }        }        return reshape;    }}

解法二

解法一的优化版本

public class Solution {    public int[][] matrixReshape(int[][] nums, int r, int c) {        if (nums == null || nums.length == 0 || r * c != nums.length * nums[0].length) {            return nums;        }        if (nums[0] == null || nums[0].length == 0) {            return nums;        }        int[][] reshape = new int[r][c];        int count = 0;        for (int i = 0; i < r; i++) {            for (int j = 0; j < c; j++) {                reshape[i][j] = nums[count / nums[0].length][count % nums[0].length];                count++;            }        }        return reshape;    }}