【LeetCode】59. Spiral Matrix II

1.题目描述

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

给定一个正整数 n，生成一个包含 1 到 n2 所有元素，且元素按顺时针顺序螺旋排列的正方形矩阵。

Example:

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

2.Solutions

public static int[][] generateMatrix(int n) {
    int[][] ret = new int[n][n];
    int left = 0,top = 0;
    int right = n -1,down = n - 1;
    int count = 1;
    while (left <= right) {

        for (int j = left; j <= right; j++) {
            ret[top][j] = count++;
        }
        top++;

        for (int i = top; i <= down; i++) {
            ret[i][right] = count++;
        }
        right--;

        for (int j = right; j >= left; j--) {
            ret[down][j] = count++;
        }
        down--;

        for (int i = down; i >= top; i--) {
            ret[i][left] = count++;
        }
        left++;
    }
    return ret;
}

参考：【LeetCode】54. Spiral Matrix

（完）