## leetcode134 Gas Station

``` 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))```

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Origin www.cnblogs.com/yawenw/p/12466640.html
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