0054-spiral-matrix.cpp

/*
    Given a matrix, return all elements in spiral order

    Set up boundaries, go outside in CW: top->right->bottom->left

    Time: O(m x n)
    Space: O(m x n)
*/

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
        int left = 0;
        int top = 0;
        int right = matrix[0].size() - 1;
        int bottom = matrix.size() - 1;
        
        vector<int> result;
        
        while (top <= bottom && left <= right) {
            for (int j = left; j <= right; j++) {
                result.push_back(matrix[top][j]);
            }
            top++;
            
            for (int i = top; i <= bottom; i++) {
                result.push_back(matrix[i][right]);
            }
            right--;
            
            if (top <= bottom) {
                for (int j = right; j >= left; j--) {
                    result.push_back(matrix[bottom][j]);
                }
            }
            bottom--;
            
            if (left <= right) {
                for (int i = bottom; i >= top; i--) {
                    result.push_back(matrix[i][left]);
                }
            }
            left++;
        }
        
        return result;
    }
};