代码：
/*** @param {number[]} gas* @param {number[]} cost* @return {number}*/
var canCompleteCircuit = function(gas, cost) {var arr = [];var curSum = 0;var positiveSum = 0;var positiveIndex = 0;var index = gas.length - 1;gas.forEach((item, index) => {arr.push(item - cost[index])});while (index >= 0) {if (arr[index] < 0) {curSum = arr[index--];while (curSum < 0 && index >= 0) {curSum += arr[index--];}if (index < 0) {if (curSum + positiveSum >= 0) {return positiveIndex}else {return -1}}else {positiveSum += curSum;positiveIndex = index + 1;curSum = 0;}}else {while (arr[index] >= 0 && index >= 0) {positiveSum += arr[index];positiveIndex = index--;}if (index < 0) {return 0}}}return -1
};