Spiral Matrix II

最新推荐文章于 2025-01-09 18:09:55 发布

violet_program

最新推荐文章于 2025-01-09 18:09:55 发布

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分类专栏： Medium Other Algorithms

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本文介绍了一种用于生成螺旋矩阵的算法实现，该算法能够根据给定的整数n生成一个n×n的矩阵，矩阵元素从1到n²按螺旋顺序填充。提供了三种不同的Java实现方式，包括基础实现、边角情况处理以及更优的编码风格。

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Given an integer n, generate a square matrix filled with elements from 1 ton² in spiral order.

For example,
Given n = 3,

You should return the following matrix:

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

1. Works only for even n. 因为无法处理最后的中心数

	public int[][] generateMatrix(int n) {
		// Start typing your Java solution below
		// DO NOT write main() function
		int[][] res = new int[n][n];
		int max = n * n;
		int counter = 1;
		int layer = 0;
		while(true){
			for(int i = layer; i < n - layer - 1; i++){
				res[layer][i] = counter;
				counter++;
			}
			if(counter > max)
				break;
			for(int i = layer; i < n - layer - 1; i++){
				res[i][n - layer - 1] = counter;
				counter++;
			}
			if(counter > max)
				break;
			for(int i = n - layer - 1; i >= layer + 1; i--){
				res[n - layer - 1][i] = counter;
				counter++;
			}
			if(counter > max)
				break;
			for(int i = n - layer - 1; i >= layer + 1; i--){
				res[i][layer] = counter;
				counter++;
			}
			if(counter > max)
				break;
			layer++;
		}
		return res;
	}

2. 稍微处理下边角，通过。

public class Solution {
    public int[][] generateMatrix(int n) {
		// Start typing your Java solution below
		// DO NOT write main() function
		int[][] res = new int[n][n];
		int max = n * n;
		int counter = 1;
		int layer = 0;
		while(true){
			for(int i = layer; i <= n - layer - 1; i++){
				res[layer][i] = counter;
				counter++;
			}
			if(counter > max)
				break;
			for(int i = layer + 1; i < n - layer - 1; i++){
				res[i][n - layer - 1] = counter;
				counter++;
			}
			if(counter > max)
				break;
			for(int i = n - layer - 1; i >= layer; i--){
				res[n - layer - 1][i] = counter;
				counter++;
			}
			if(counter > max)
				break;
			for(int i = n - layer - 2; i >= layer + 1; i--){
				res[i][layer] = counter;
				counter++;
			}
			if(counter > max)
				break;
			layer++;
		}
		return res;
	}
}

3. Better coding style

public class Solution {
    public int[][] generateMatrix(int n) {
		// Start typing your Java solution below
		// DO NOT write main() function
		int[][] res = new int[n][n];
		if (n == 0)
			return res;
		int num = 0;
		int layer = n / 2;
		for (int i = 0; i < layer; ++i) {
			int j;
			for (j = i; j < n - 1 - i; ++j)
				res[i][j] = ++num;
			for (j = i; j < n - 1 - i; ++j)
				res[j][n - 1 - i] = ++num;
			for (j = n - 1 - i; j > i; --j)
				res[n - 1 - i][j] = ++num;
			for (j = n - 1 - i; j > i; --j)
				res[j][i] = ++num;
		}
		if (n % 2 == 1)
			res[n / 2][n / 2] = ++num;
		return res;
	}
}