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Spiral Matrix

This question is part of NeetCode150 series.

Problem Description

Given an m x n matrix, return all elements of the matrix in spiral order.

leetcode

Solution

Spiral Traversal

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class Solution {

    public List<Integer> spiralOrder(int[][] matrix) {

        int n = matrix.length;
        int m = matrix[0].length;

        int startRow = 0;
        int endRow = n-1;
        int startColumn = 0;
        int endColumn = m-1;

        List<Integer> list = new ArrayList<>();

        //print the values at the perimeter, then do the same for the inner rectangles
        while(startRow <= endRow && startColumn <= endColumn){

            for(int i=startColumn; i<=endColumn; i++){
                list.add(matrix[startRow][i]);
            }

            for(int i=startRow+1; i<=endRow; i++){
                list.add(matrix[i][endColumn]);
            }

            for(int i=endColumn-1; i>=startColumn; i--){

                //edge case: when there is a single row in the middle
                //this will be traversed in the first for loop, so we can break if that happens
                if(startRow == endRow) break;
                list.add(matrix[endRow][i]);
            }

            for(int i=endRow-1; i>=startRow+1; i--){

                //edge case: when there is a single column in the middle
                //this will be traversed in the second for loop, so we can break if that happens
                if(startColumn == endColumn) break;
                list.add(matrix[i][startColumn]);
            }

            startRow++; startColumn++;
            endRow--; endColumn--;

        }

        return list;

    }

}
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