Circular tour

The Circular Tour problem is a classic computer science problem, which involves finding a starting point in a circular route, from where one can complete the tour without running out of fuel.

def circular_tour(petrol, distance):
    n = len(petrol)
 
    start = 0
    end = 1
 
    current_petrol = petrol[start] - distance[start]
 
    while start != end or current_petrol < 0:
        while current_petrol < 0 and start != end:
            current_petrol -= petrol[start] - distance[start]
            start = (start + 1) % n
 
            if start == 0:
                return -1
 
        current_petrol += petrol[end] - distance[end]
        end = (end + 1) % n
 
    return start
 
# Example usage:
petrol = [4, 6, 7, 4]
distance = [6, 5, 3, 5]
start = circular_tour(petrol, distance)
print("Starting point:", start) # Output: Starting point: 2