docs: add problem description for Leetcode 134

Author: bujosa

src/medium/readme.md

@@ -1032,6 +1032,57 @@ Put the code below in main.rs and run `cargo run`
     println!("result: {:?}", result);
 ```
 
+# 134. Gas Station
+
+## Description
+
+There are n gas stations along a circular route, where the amount of gas at the ith station is gas[i].
+
+You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i + 1)th station. You begin the journey with an empty tank at one of the gas stations.
+
+Given two integer arrays gas and cost, return the starting gas station's index if you can travel around the circuit once in the clockwise direction, otherwise return -1. If there exists a solution, it is guaranteed to be unique
+
+## Examples
+
+```text
+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.
+```
+
+```text
+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.
+```
+
+## How to Run in main.rs
+
+Put the code below in main.rs and run `cargo run`
+
+```rust
+  let gas = vec![1, 2, 3, 4, 5];
+  let cost = vec![3, 4, 5, 1, 2];
+  let result = leetcode::medium::gas_station::can_complete_circuit(gas, cost);
+  println!("result: {}", result);
+```
+
+
 # 138. Copy List with Random Pointer
 
 ## Description