LeetCode 134. Gas Station(java)
阿新 • • 發佈:2018-12-30
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, otherwise return -1.
Note:
The solution is guaranteed to be unique.
解法:這道題的重點在於理解:當車從i跑不到j的時候,那麼從i到j的中間任何一點也都跑不到j,因為能跑到某個站的前提是現有汽油數大於等於消耗數,因此這道題的思路就是,從0開始跑,直到跑不到i,那麼就從i重新跑,直到從某個位置j能跑到0,這時候我們再檢查從0能不能跑到j,如果可以就返回j,不可以則返回-1,程式碼如下:
public int canCompleteCircuit(int[] gas, int[] cost) {
int gass = gas[0], start = 0 ;
for (int i = 0; i < gas.length - 1; i++) {
gass -= cost[i];
if (gass >= 0) {
gass += gas[i+1];
} else {
start = i + 1;
gass = gas[i + 1];
}
}
gass -= cost[gas.length - 1];
if (gass < 0) {
return -1;
}
gass += gas[0];
for (int i = 0; i < start; i++) {
gass -= cost[i];
if (gass >= 0) {
gass += gas[i+1];
} else {
return -1;
}
}
return start;
}