Gas Station.cpp

/* Leet Code */
/* Title - Gas Station */
/* Created By - Akash Modak */
// /* Date - 08/06/2023 */

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

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

// Given two integer arrays gas and cost, return the starting gas station's index if you can travel around the circuit once in the clockwise direction, otherwise return -1. If there exists a solution, it is guaranteed to be unique

 

// 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.

class Solution {
public:
    int canCompleteCircuit(vector<int>& gas, vector<int>& cost) {
        int start=0, currGas=0,totalGas=0;
        for(int i=0;i<cost.size();i++){
            currGas+=gas[i]-cost[i];
            totalGas+=gas[i]-cost[i];
            if(currGas<0) start=i+1,currGas=0;
        }
        return totalGas>=0?start:-1;
    }
};