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【LeetCode】Gas Station

Gas Station

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, otherwise return -1.

Note:
The solution is guaranteed to be unique.

 

思路:顺序扫一圈。如果总油量小于总消耗,说明起点错误,则将起点往后移位。

几个地方需要注意:

1、如果有解,则终点绕一圈之后回到起点

2、最多绕一圈即可判断是有解还是无解,起点重复代表无解

3、终点必须在起点之后

class Solution {public:    int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {        vector<int>::size_type size = gas.size();        int start = 0;        int finish = 0;        int totalGas = gas[start];        int totalCost = cost[start];        while(finish != start+size)        {//if finish == start+size, finish            if(totalGas >= totalCost)            {                finish ++;                totalGas += gas[finish%size];                totalCost += cost[finish%size];            }            else            {                totalGas -= gas[start];                totalCost -= cost[start];                start ++;                if(start == size)                    return -1;  //no solution                //restart here                if(finish+1 == start)                {                    finish ++;                    totalGas = gas[start];                    totalCost = cost[start];                }            }        }        return start;    }};

【LeetCode】Gas Station