LeetCode 59. Spiral Matrix II

[woodyiiiiiii]

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

Example 1:

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

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跟I题一样的思路。又因为这是正方形矩阵，中间的剩余部分的边界判断可以省略。

class Solution {
    public int[][] generateMatrix(int n) {
        int[][] matrix = new int[n][n];
        if (n == 0) {
            return matrix;
        }
        int left = 0, right = n - 1, top = 0, bottom = n - 1;
        int i = 0, j = 0;
        int val = 1;
        while (left <= right && top <= bottom) {
            for (j = left; j <= right; ++j) {
                matrix[top][j] = val++;
            }
            if (top == bottom) {
                break;
            }
            for (i = top + 1; i <= bottom; ++i) {
                matrix[i][right] = val++;
            }
            if (left == right) {
                break;
            }
            for (j = right - 1; j >= left; --j) {
                matrix[bottom][j] = val++;
            }
            for (i = bottom - 1; i > top; --i) {
                matrix[i][left] = val++;
            }
            ++left;
            ++top;
            --right;
            --bottom;
        }
        
        return matrix;
    }
}

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参考资料:
LeetCode原题