LeetCode 134: Gas Station Solution

Problem Explanation

Explanation:

To solve this problem, we can use the concept of a circular trip. We iterate over all gas stations and calculate the total gas left after reaching each station. If at any point the total gas becomes negative, we reset our starting station to the next station and reset the total gas to 0.

Algorithm:

Initialize variables totalGas and startStation to 0.
Iterate over all gas stations:
- Calculate the total gas by adding the gas at the current station and subtracting the cost to reach the next station.
- If the total gas becomes negative, update startStation to the next station and reset totalGas to 0.
After completing the loop, check if the total gas is non-negative. If yes, return the startStation, otherwise return -1.

Time Complexity: O(n) - We iterate over all gas stations once. Space Complexity: O(1) - We use only a constant amount of extra space.

Solution Code

class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int totalGas = 0;
        int totalCost = 0;
        int startStation = 0;
        int tank = 0;
        
        for (int i = 0; i < gas.length; i++) {
            totalGas += gas[i];
            totalCost += cost[i];
            tank += gas[i] - cost[i];
            if (tank < 0) {
                startStation = i + 1;
                tank = 0;
            }
        }
        
        return totalGas >= totalCost ? startStation : -1;
    }
}

Frequently Asked Questions

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