/**
 * https://leetcode.cn/problems/gas-station/?envType=study-plan-v2&envId=top-interview-150
 * @param {number[]} gas
 * @param {number[]} cost
 * @return {number}
 */
const canCompleteCircuit = function (gas, cost) {
  let totalGas = 0; let
    totalCost = 0;
  let currentGas = 0;
  let start = 0;

  for (let i = 0; i < gas.length; i++) {
    totalGas += gas[i];
    totalCost += cost[i];

    currentGas += gas[i] - cost[i];

    // 如果油量不足，更新起点为下一个加油站
    if (currentGas < 0) {
      start = i + 1;
      currentGas = 0;
    }
  }

  // 如果总油量小于总油耗，无法完成一圈
  return totalGas < totalCost ? -1 : start;
};