螺旋矩阵

/*
 * 思路：
 * 1. 利用Stream流的特性实现螺旋遍历。
 * 2. 通过Stream.of()创建流，按顺序访问矩阵的四个边界元素。
 * 3. 利用flatMap和collect方法，将遍历结果收集到列表中。
 */
 
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
 
public class SpiralOrderStream {
    public List<Integer> spiralOrder(int[][] matrix) {
        if (matrix == null || matrix.length == 0) return new ArrayList<>();
        List<Integer> result = new ArrayList<>();
        int m = matrix.length, n = matrix[0].length;
        int left = 0, right = n - 1, top = 0, bottom = m - 1;
        while (left <= right && top <= bottom) {
            Stream.of(
                IntStream.rangeClosed(left, right).map(i -> matrix[top][i]).boxed().collect(Collectors.toList()),
                IntStream.rangeClosed(top + 1, bottom).map(i -> matrix[i][right]).boxed().collect(Collectors.toList()),
                IntStream.rangeClosed(left, right).map(i -> matrix[bottom][right - i + left]).boxed().collect(Collectors.toList()),
                IntStream.rangeClosed(top + 1, bottom).map(i -> matrix[bottom - i + top + 1][left]).boxed().collect(Collectors.toList())
            ).flatMap(List::stream).forEach(result::add);
            top++; right--; bottom--; left++;
        }
        return result;
    }
}