Spiral Matrix

1package pkg5leetcode.blind75;2 3/*4 * Spiral Matrix | LC 545 * APPROACH: Layer-by-layer traverse top/bottom/left/right bounds.6 * COMPLEXITY: Time O(mn), Space O(1) excluding output7 */8import java.util.*;9 10public class blind75_LC54SpiralMatrix {11    static List<Integer> spiralOrder(int[][] matrix) {12        List<Integer> res = new ArrayList<>();13        int top = 0, bottom = matrix.length - 1, left = 0, right = matrix[0].length - 1;14        while (top <= bottom && left <= right) {15            for (int j = left; j <= right; j++) res.add(matrix[top][j]);16            top++;17            for (int i = top; i <= bottom; i++) res.add(matrix[i][right]);18            right--;19            if (top <= bottom) {20                for (int j = right; j >= left; j--) res.add(matrix[bottom][j]);21                bottom--;22            }23            if (left <= right) {24                for (int i = bottom; i >= top; i--) res.add(matrix[i][left]);25                left++;26            }27        }28        return res;29    }30 31    public static void main(String[] args) {32        check(spiralOrder(new int[][]{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}).equals(Arrays.asList(1, 2, 3, 6, 9, 8, 7, 4, 5)), "case1");33        check(spiralOrder(new int[][]{{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}}).equals(Arrays.asList(1, 2, 3, 4, 8, 12, 11, 10, 9, 5, 6, 7)), "case2");34        System.out.println("all tests passed");35    }36 37    static void check(boolean cond, String name) {38        if (!cond) throw new AssertionError("FAILED: " + name);39        System.out.println("  PASS " + name);40    }41}