[LeetCode] 59. Spiral Matrix II

ProblemGiven a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.Example:Input: 3Output:[ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5 ]]Solutionclass Solution { public int[][] generateMatrix(int n) { int[][] res = new int[n][n]; if (n == 0) return res; int num = 1, rStart = 0, rEnd = n-1, cStart = 0, cEnd = n-1; while (rStart <= rEnd && cStart <= cEnd) { for (int j = cStart; j <= cEnd; j++) res[rStart][j] = num++; rStart++; for (int i = rStart; i <= rEnd; i++) res[i][cEnd] = num++; cEnd–; for (int j = cEnd; j >= cStart; j–) { if (rStart > rEnd) break; res[rEnd][j] = num++; } rEnd–; for (int i = rEnd; i >= rStart; i–) { if (cStart > cEnd) break; res[i][cStart] = num++; } cStart++; } return res; }}