LC134. Gas Station

class Solution:
    def canCompleteCircuit(self, gas: List[int], cost: List[int]) -> int:
        """ time O(N)   space O(1)
    1. loop through gas, cost array, get total gas, total cost
    2. during iteration, check current tank < 0, if yes, reset current tank, start from i + 1 
    3. check if total cost <= total gas
       
        """
        n = len(gas) 
        sumCost = 0
        sumGas = 0
        start = 0
        tank = 0     
        for i,(g,c) in enumerate(zip(gas,cost)):
            sumCost += c
            sumGas += g
            tank +=  g - c 
            if tank < 0:
                start = i + 1
                tank = 0
        if sumCost > sumGas:
            return -1
        return start