1 """ 2 There are N gas stations along a circular route, where the amount of gas at station i is gas[i]. 3 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. 4 Return the starting gas station's index if you can travel around the circuit once in the clockwise direction, otherwise return -1. 5 Note: 6 If there exists a solution, it is guaranteed to be unique. 7 Both input arrays are non-empty and have the same length. 8 Each element in the input arrays is a non-negative integer. 9 Example 1: 10 Input: 11 gas = [1,2,3,4,5] 12 cost = [3,4,5,1,2] 13 Output: 3 14 Explanation: 15 Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 16 Travel to station 4. Your tank = 4 - 1 + 5 = 8 17 Travel to station 0. Your tank = 8 - 2 + 1 = 7 18 Travel to station 1. Your tank = 7 - 3 + 2 = 6 19 Travel to station 2. Your tank = 6 - 4 + 3 = 5 20 Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3. 21 Therefore, return 3 as the starting index. 22 Example 2: 23 Input: 24 gas = [2,3,4] 25 cost = [3,4,3] 26 Output: -1 27 Explanation: 28 You can't start at station 0 or 1, as there is not enough gas to travel to the next station. 29 Let's start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 30 Travel to station 0. Your tank = 4 - 3 + 2 = 3 31 Travel to station 1. Your tank = 3 - 3 + 3 = 3 32 You cannot travel back to station 2, as it requires 4 unit of gas but you only have 3. 33 Therefore, you can't travel around the circuit once no matter where you start. 34 """ 35 "" " 36 Solution a: own the AC 37 [ accordance with the subject claim to achieve normal 38 is " "" 39 class Solution1: 40 DEF canCompleteCircuit (Self, Gas, cost): 41 is CUR = 0 42 is for I in Range (len (Gas)) : 43 is CUR = Gas [I] 44 is for J in Range (I, I + len (Gas)): 45 CUR - = cost [J% len (Gas)] 46 is IF CUR < 0: 47 BREAK 48 CUR + = Gas [ (j + 1)%len (Gas)] 49 IF CUR> = 0: 50 return I 51 is return -1 52 is "" " 53 is Solution II: ALGORITHM, comply with two main principles: 54 1. The starting point must satisfy gas> cost, it is impossible to start 55 2. the overall gas> cost, or must go finish 56 is "" " 57 is class Solution: 58 DEF canCompleteCircuit (Self, Gas, cost): 59 total = 0 60 RES = 0 61 is CUR = 0 62 is for I in Range (len (Gas)): 63 cur += gas[i] - cost[i] 64 if cur < 0: 65 res = i + 1 66 total += cur 67 cur = 0 68 return res if (total + cur) >= 0 else -1 69 if __name__ == '__main__': 70 gas = [1, 2, 3, 4, 5] 71 cost = [3, 4, 5, 1, 2] 72 ans = Solution1() 73 print(ans.canCompleteCircuit(gas, cost))