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 ] ] //TC=O(n^2) public class Solution { public int[][] generateMatrix(int n) { //special case if(n==0) return new int[0][0]; int[][] res = new int[n][n]; int num = 1; int top=0, right=n-1, bottom=n-1, left=0; while(top<bottom){ //上边框 for(int i=left; i<right; i++){ res[top][i]=num; num++; } //右边框 for(int i=top; i<bottom; i++){ res[i][right]=num; num++; } //下边框 for(int i=right; i>left; i--){ res[bottom][i]=num; num++; } //左边框 for(int i=bottom; i>top; i--){ res[i][left]=num; num++; } //这里容易遗漏 top++; right--; bottom--; left++; } //when top=bottom, it comes to the center if(num==n*n) res[top][top]=num; return res; } }
