Matrix traversal in spiral order (left to right)

spiral_lr.cpp

vector<int> spiralOrder(const vector<vector<int>> &A) {
    vector<int> result;
    int i = 0, j = 0;
    int startI = 0, startJ = 1;
    int rows = A.size();
    int cols = A[0].size();
    int total = rows*cols;    
        
    while (result.size() < total) {
        // over a row
        for (; i < cols; i++) {
            if (result.size() == total)
                return result;
            result.push_back(A[j][i]);
        }
        
        // over a column 
        for (i--, j++; j < rows; j++) {
            if (result.size() == total)
                return result;
            result.push_back(A[j][i]);
        }
        
        // go back in a row   
        for (j--, i--; i >= startI; i--) {
            if (result.size() == total)
                return result;
            result.push_back(A[j][i]);
        }
        
        // go back in a column (avoid last item)        
        for (i++, j--; j >= startJ; j--) {
            if (result.size() == total)
                return result;
            result.push_back(A[j][i]);
        }
        
        // restrict to inner rectangle and repeat
        i++;j++;
        startI++;startJ++;
        cols--; rows--;
    }    	
	
	return result;
}