SpiralTraversal.java

import java.util.*;

// O(m * n) time, O(1) space
class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> ans = new ArrayList<>();

        int n = matrix.length;
        int m = matrix[0].length;
        int top = 0;
        int left = 0;
        int bottom = n-1;
        int right = m-1;

        while (top <= bottom && left <= right) {

            for (int i = left; i <= right; i++) {
                ans.add(matrix[top][i]);
            }
            top++;

            for (int i = top; i <= bottom; i++) {
                ans.add(matrix[i][right]);
            }
            right--;

            if (top <= bottom) {
                for (int i = right; i >= 0; i--) {
                    ans.add(matrix[bottom][i]);
                }
                bottom--;
            }

            if (left <= right) {
                for (int i = bottom; i >= top; i--) {
                    ans.add(matrix[i][left]);
                }
                left++;
            }
        }
        return ans;
    }
}