Find the Unique Start for a Circular Fuel Circuit
Company: Amazon
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Other
### Problem
Along a clockwise circular route, station `i` supplies `gas[i]` units and traveling to the next station costs `cost[i]`. Choose a zero-based starting station, begin with an empty unlimited-capacity tank, and collect gas whenever visiting a station. Return the starting index if a full circuit is possible, otherwise -1. If a valid start exists, it is guaranteed to be unique.
```cpp
int canCompleteCircuit(vector<int>& gas, vector<int>& cost);
```
### Examples
```text
Input: gas = [2,0,4], cost = [3,1,2]
Output: 2
```
Starting at 2 leaves successive post-travel balances 2,1,0.
```text
Input: gas = [1,2], cost = [2,2]
Output: -1
```
### Constraints
- Both arrays have the same length, between 1 and 100000.
- Each amount and cost is between 0 and 10000, inclusive.
- A feasible starting index, when present, is unique.
Overview: Find the unique feasible circular gas-route start by discarding failed segments and checking total net supply.
