[4]54. Spiral Matrix/59. Spiral Matrix II(Java)

54. Spiral Matrix

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

For example,
Given the following matrix:

[ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ]]

You should return [1,2,3,6,9,8,7,4,5].

class Solution {    public List<Integer> spiralOrder(int[][] matrix) {        List<Integer> res = new ArrayList<>();        if (matrix.length == 0)             return res;        int rowBegin = 0, colBegin = 0;        int rowEnd = matrix.length - 1;        int colEnd = matrix[0].length - 1;        while (rowBegin <= rowEnd && colBegin <= colEnd) {            // Traverse right            for (int j = colBegin; j <= colEnd; j ++) {                res.add(matrix[rowBegin][j]);            }            rowBegin ++;            // Traverse down            for (int i = rowBegin; i <= rowEnd; i ++) {                res.add(matrix[i][colEnd]);            }            colEnd --;            if (rowBegin <= rowEnd) {                // Traverse left                for (int j = colEnd; j >= colBegin; j --) {                    res.add(matrix[rowEnd][j]);                }                rowEnd --;            }            if (colBegin <= colEnd) {                // Traverse up                for (int i = rowEnd; i >= rowBegin; i --) {                    res.add(matrix[i][colBegin]);                }                colBegin ++;            }        }        return res;    }}

59. Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

For example,
Given n = 3,

You should return the following matrix:

[ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5 ]]

class Solution {    public int[][] generateMatrix(int n) {        int[][] matrix = new int[n][n];        if (n == 0) return matrix;                int rowBegin = 0, colBegin = 0;        int rowEnd = n - 1, colEnd = n - 1;        int num = 1;        while (rowBegin <= rowEnd && colBegin <= colEnd) {            // Traverse right            for (int j = colBegin; j <= colEnd; j ++) {                matrix[rowBegin][j] = num ++;            }            rowBegin ++;            // Traverse down            for (int i = rowBegin; i <= rowEnd; i ++) {                matrix[i][colEnd] = num ++;            }            colEnd --;            if (rowBegin <= rowEnd) {                // Traverse left                for (int j = colEnd; j >= colBegin; j --) {                    matrix[rowEnd][j] = num ++;                }                rowEnd --;            }            if (colBegin <= colEnd) {                // Traverse up                for (int i = rowEnd; i >= rowBegin; i --) {                    matrix[i][colBegin] = num ++;                }                colBegin ++;            }        }        return matrix;    }}