Leetcode 54

Working with matrix can be challenging, in this question, the main thing is attention to detail, making sure adding no duplicate items and shrink the boundry.

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new ArrayList<>();
        int m = matrix.length;
        int n = matrix[0].length;
        int up = 0;
        int down = m - 1;
        int left = 0;
        int right = n - 1;

        while(res.size() < m * n){
            // there is more item to traverse
            // first we add everthing from left to right
            for(int i = left; i <= right; i ++){
                res.add(matrix[up][i]);
            }
            // now we add from up to down 
            for(int j = up + 1; j <= down; j ++){
                res.add(matrix[j][right]);
            }
            // going from right to left but we got to make sure up != down that way we not adding duplicate row
            if(up != down){
                for(int i = right - 1; i >= left; i --){
                    res.add(matrix[down][i]);
                }
            }
            // from bot to top
            if(left != right){
                // note we dont want to add matrix[up][left] it is added from the left to right traversal!
                for(int j = down - 1; j > up; j --){
                    res.add(matrix[j][left]);
                }
            }

            // now we just have to shrink the boundry
            left ++;
            right --;
            up ++;
            down --;
        }
        return res;
    }
}