_0134_GasStation.java

package com.diguage.algorithm.leetcode;

/**
 * = 134. Gas Station
 *
 * https://leetcode.com/problems/gas-station/[Gas Station - LeetCode]
 *
 * 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 in the clockwise direction, otherwise return -1.
 *
 * *Note:*
 *
 * * If there exists a solution, it is guaranteed to be unique.
 * * Both input arrays are non-empty and have the same length.
 * * Each element in the input arrays is a non-negative integer.
 *
 * .Example 2:
 * [source]
 * ----
 * 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:
 * [source]
 * ----
 * 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.
 * ----
 *
 * @author D瓜哥, https://www.diguage.com/
 * @since 2020-01-25 21:55
 */
public class _0134_GasStation {
    /**
     * Runtime: 0 ms, faster than 100.00% of Java online submissions for Gas Station.
     *
     * Memory Usage: 39.1 MB, less than 5.88% of Java online submissions for Gas Station.
     *
     * Copy from: https://leetcode-cn.com/problems/gas-station/solution/jia-you-zhan-by-leetcode/[加油站 - 加油站 - 力扣（LeetCode）]
     */
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int n = gas.length;
        int totalTank = 0;
        int currentTank = 0;
        int startStation = 0;
        for (int i = 0; i < n; i++) {
            totalTank += gas[i] - cost[i];
            currentTank += gas[i] - cost[i];
            if (currentTank < 0) {
                startStation = i + 1;
                currentTank = 0;
            }
        }
        return totalTank >= 0 ? startStation : -1;
    }

    public static void main(String[] args) {
        _0134_GasStation solution = new _0134_GasStation();
        int[] g1 = {1, 2, 3, 4, 5};
        int[] c1 = {3, 4, 5, 1, 2};
        int r1 = solution.canCompleteCircuit(g1, c1);
        System.out.println((r1 == 3) + " : " + r1);
    }
}