134. Gas Station

class Solution:
    def canCompleteCircuit(self, gas: List[int], cost: List[int]) -> int:
        if sum(gas) < sum(cost):
            return -1
        
        i = 0
        j = 0

        while i < len(gas):
            total = 0

            while i < len(gas) and gas[i] - cost[i] < 0:
                i += 1
            
            j = i

            while i < len(gas) and total >= 0:
                total += gas[i]
                total -= cost[i]
                i += 1
        
        return j