0054. Spiral Matrix.md

54. Spiral Matrix, medium

tags: review

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

Example 1:

Input:
[
 [ 1, 2, 3 ],
 [ 4, 5, 6 ],
 [ 7, 8, 9 ]
]
Output: [1,2,3,6,9,8,7,4,5]
Example 2:

Input:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
        if (matrix.empty() || matrix[0].empty())
            return vector<int>();
        
        vector<int> res;
        int m = matrix.size();
        int n = matrix[0].size();
        int layer = 0;
        int i = 0, j = 0;
        while(layer <= (min(m,n)-1)/2) {
            res.push_back(matrix[i][j]);
            // to right
            if (j < n - layer) {
                j++;
                while(j < n - layer) {
                    res.push_back(matrix[i][j]);
                    j++;
                }
                j--;
            }
            // to bottom
            if (i >= m - 1 - layer)
                break;
            i++;
            while (i < m - layer) {
                res.push_back(matrix[i][j]);
                i++;
            }
            i--;
            
            // to left
            if (j <= layer)
                break;
            j--;
            while (j >= layer) {
                res.push_back(matrix[i][j]);
                j--;
            }
            j++;
            
            // to top
            if (i <= layer)
                break;
            i--;
            while (i > layer) {
                res.push_back(matrix[i][j]);
                i--;
            }
            layer++;
            i = layer;
            j = layer;
        }
        return res;
    }
};