Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order. For example, Given the following matrix: [ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ] You should return [1,2,3,6,9,8,7,4,5]. http://leetcode.com/onlinejudge#question_54

leetcode_spiral_matrix.cpp

#define INF 0x7fffffff

int dir[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};

bool inBound(int x, int y, int n, int m) {
    return x >= 0 && x < n && y >= 0 && y < m;
}

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int> > &matrix) {
        vector<int> ans;
        int n = matrix.size();
        if (n == 0)
            return ans;
        int m = matrix[0].size();
        if (m == 0)
            return ans;
        int x = 0, y = 0;
        int d = 0;
        for (int i = 0; i < n * m; ++i) {
            if (i != 0) {
                while (true) {
                    int nx = x + dir[d][0], ny = y + dir[d][1];
                    if (inBound(nx, ny, n, m) && matrix[nx][ny] != INF) {
                        x = nx;
                        y = ny;
                        break;
                    }
                    d = (d + 1) % 4;
                }
            }
            ans.push_back(matrix[x][y]);
            matrix[x][y] = INF;
        }
        return ans;
    }
};