LeetCode59-螺旋矩阵II

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题目链接

英文链接：https://leetcode.com/problems/spiral-matrix-ii/

中文链接：https://leetcode-cn.com/problems/spiral-matrix-ii/

题目详述

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。

示例:

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

题目详解

与 LeetCode54-螺旋矩阵 类似，都是按层进行处理，处理完一层，再处理下一层。

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public class LeetCode_00059 {

    public int[][] generateMatrix(int n) {
        int[][] res = new int[n][n];
        int top = 0, bottom = n - 1;
        int left = 0, right = n - 1;
        int num = 1;
        while (top <= bottom && left <= right) {
            num = fillEdge(res, top++, bottom--, left++, right--, num);
        }
        return res;
    }

    private int fillEdge(int[][] res, int top, int bottom, int left, int right, int num) {
        if (top == bottom) {
            for (int i = left; i <= right; ++i) {
                res[top][i] = num++;
            }
        } else if (left == right) {
            for (int i = top; i <= bottom; ++i) {
                res[i][right] = num++;
            }
        } else {
            int i = top, j = left;
            while (j != right) {
                res[i][j++] = num++;
            }
            while (i != bottom) {
                res[i++][j] = num++;
            }
            while (j != left) {
                res[i][j--] = num++;
            }
            while (i != top) {
                res[i--][j] = num++;
            }
        }
        return num;
    }
}