There are N gas stations along a circular route, where the amount of gas at station i is gas[i].

You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from station i to its next station (i+1). You begin the journey with an empty tank at one of the gas stations.

Return the starting gas station's index if you can travel around the circuit once in the clockwise direction, otherwise return -1.

Note:


       If there exists a solution, it is guaranteed to be unique.
       Both input arrays are non-empty and have the same length.
       Each element in the input arrays is a non-negative integer.


Example 1:


Input: 
gas  = [1,2,3,4,5]
cost = [3,4,5,1,2]

Output: 3

Explanation:
Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4
Travel to station 4. Your tank = 4 - 1 + 5 = 8
Travel to station 0. Your tank = 8 - 2 + 1 = 7
Travel to station 1. Your tank = 7 - 3 + 2 = 6
Travel to station 2. Your tank = 6 - 4 + 3 = 5
Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3.
Therefore, return 3 as the starting index.


Example 2:


Input: 
gas  = [2,3,4]
cost = [3,4,3]

Output: -1

Explanation:
You can't start at station 0 or 1, as there is not enough gas to travel to the next station.
Let's start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4
Travel to station 0. Your tank = 4 - 3 + 2 = 3
Travel to station 1. Your tank = 3 - 3 + 3 = 3
You cannot travel back to station 2, as it requires 4 unit of gas but you only have 3.
Therefore, you can't travel around the circuit once no matter where you start.

Difficulty: interview

Starter code:

class Solution:
    def canCompleteCircuit(self, gas: List[int], cost: List[int]) -> int:
        

Solutions:
class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         if sum(gas) < sum(cost):
             return -1
         Rest = 0
         index = 0
         for i in range(len(gas)):
             Rest += gas[i] - cost[i]
             if Rest < 0:
                 index = i + 1
                 Rest = 0
         return index

class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         if sum(gas) < sum(cost):
             return -1
         
         totalGas = 0
         position = 0
         for i in range(len(gas)):
             totalGas += gas[i] - cost[i]
             
             if totalGas < 0:
                 totalGas = 0
                 position = i + 1
         
         return position


class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         if not gas:
             return -1
         if len(gas) == 1:
             return 0 if gas[0] >= cost[0] else -1
         
         diff = [gas[i] - cost[i] for i in range(len(gas))]
         
         print(diff)
         
         start = []
         for i in range(len(diff)):
             if diff[i] < 0 and diff[(i + 1) % len(diff)] >= 0:
                 start.append((i + 1) % len(diff))
         
         if not start:
             start = [0]
         
         print(start)
         
         for i in start:
             bal = diff[i]
             ptr = (i + 1) % len(diff)
             while ptr != i:
                 bal += diff[ptr]
                 ptr = (ptr + 1) % len(diff)
                 if bal < 0:
                     break
             if bal >= 0:
                 return i
         return -1
             


class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
 
         st, ed, cur, n, loop = 0, -1, 0, len(gas), False
         while True:
             ed += 1
             if ed >= n: ed -= n
             while cur + gas[ed] - cost[ed] >= 0:
                 cur += gas[ed] - cost[ed]
                 ed += 1
                 if ed >= n:
                     if loop: return -1
                     ed -= n
                     loop = True
                 if ed >= st and loop: return st
             cur, st = 0, ed + 1
             if st >= n: return -1

class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         tank = 0
         total = len(gas)
         travel = 0
 
         start = -total
         current = start
         print(('start:',start))
         while travel < total:
             tank += gas[current]-cost[current]
             travel += 1
             current += 1
             if current == total:
                 return -1
             print((current,'\ttank:',tank,gas[current],cost[current],'\ttravel:',travel))
             if tank<0:
                 tank = 0
                 jump = current - start
                 start += jump
                 travel -= jump
                 print(('reset Start:', start, tank))
         return start+total


class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         n = len(gas)
         
         i = 0
         while i < n:
             total_gas = 0
             j = 0
             while j < n and total_gas >= 0:
                 index = (i + j) % n
                 total_gas += gas[index] - cost[index]
                 j += 1
             if total_gas >= 0:
                 return i
             i += j
         
         return -1


class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         cf, s, e = 0,0,0
         found = False
         while True:
             nextHop = gas[e] - cost[e]
             if cf + nextHop >= 0:
                 e = (e+1)%len(gas)
                 cf = cf + nextHop
                 if s == e :
                     found = True
                     break
                 else:
                     continue
             else:
                 if s == e:
                     s = (s+1)%len(gas)
                     e = s
                 else:
                     cf += -gas[s] + cost[s]
                     s = (s+1)%len(gas)
                 if s == 0: break
         return s if found else -1

class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         n = len(gas)
         
         i = 0
         while i < n:
             total_gas = 0
             j = 0
             while j < n and total_gas >= 0:
                 index = (i + j) % n
                 total_gas += gas[index] - cost[index]
                 j += 1
             if total_gas >= 0:
                 return i
             while i < n and gas[i] - cost[i] >= 0:
                 i += 1
             i += 1
         
         return -1


class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         res = []
         for i in range(len(gas)):
             res.append(gas[i]-cost[i])
         max_sum = 0
         max_index = 0
         a = [0 for x in range(len(res))]
         for i in range(len(res)) :
             max_sum = max(res[i]+max_sum,res[i])
             if max_sum == res[i]:
                 max_index = i
                 max_sum = res[i]
         temp = (max_index+1)%len(gas)
         gas_sum = res[max_index]
         while temp != max_index:
             gas_sum += res[temp]
             temp = (temp+1)%len(gas)
         if gas_sum>=0:
             return max_index
         else:
             return -1

class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         # if len(gas) < 2:
         #     return gas[0]
         fuel = totalGas = totalCost = start = 0
         for i in range(len(cost)):
             totalGas += gas[i]
             totalCost += cost[i]
             fuel = fuel + gas[i] - cost[i]
             if fuel < 0:
                 start = i + 1
                 fuel = 0
                 
         return start if totalGas>=totalCost else -1


class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         if sum(gas)< sum(cost):
             return -1
         rest = 0
         position = 0
         for i in range(len(gas)):
             rest += gas[i]-cost[i]
             if rest < 0:
                 rest = 0
                 position = i+1
         return position
             
 
                 


class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
 
         st, ed, cur, n, loop = 0, -1, 0, len(gas), False
         while True:
             ed += 1
             if ed >= n: ed -= n
             while cur + gas[ed] - cost[ed] >= 0:
                 cur += gas[ed] - cost[ed]
                 ed += 1
                 if ed >= n:
                     if loop: return -1
                     ed -= n
                     loop = True
                 if ed >= st and loop: return st
             cur, st = 0, ed + 1
             if st >= n: return -1

class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         left = [gas[i]-cost[i] for i in range(len(gas))]
         if sum(left) < 0:
             return -1
         tank, start = 0, 0
         for i in range(len(left)):
             tank += left[i]
             if tank < 0:
                 start = i+1
                 tank = 0
         return start

class Solution:
     def canCompleteCircuit(self, gas, cost):
         """
         :type gas: List[int]
         :type cost: List[int]
         :rtype: int
         """
         
         if len(gas) == 1:
             if cost[0] > gas[0]:
                 return -1
             else:
                 return 0
 
         sub = [g - c for (g, c) in zip(gas, cost)]
         s = 0
         e = 1
         left = sub[0]
         while e != s:
             if left >= 0:
                 left += sub[e]
                 e = (e + 1) % len(gas)
                 if e==s and left<0:
                     return -1
             else:
                 while left < 0:
                     s = (s - 1) % len(gas)
                     left += sub[s]
                     if s == (e - 1) % len(gas):
                         return -1
         return s