java: add «134. Gas Station»

URL:	https://leetcode.com/problems/gas-station/
Signed-off-by: Matej Focko <me@mfocko.xyz>

java/gas-station.java

@@ -0,0 +1,26 @@
+class Solution {
+  public int canCompleteCircuit(int[] gas, int[] cost) {
+    int totalGas = 0, totalCost = 0;
+
+    int currentGas = 0, start = 0;
+    for (var i = 0; i < gas.length; ++i) {
+      totalGas += gas[i];
+      totalCost += cost[i];
+
+      currentGas += gas[i] - cost[i];
+      if (currentGas < 0) {
+        // we can't reach this point, have to start from the next one
+        currentGas = 0;
+        start = i + 1;
+      }
+    }
+
+    if (totalGas < totalCost) {
+      // not enough gas from any station
+      return -1;
+    }
+
+    // there's a unique solution, iff it exists
+    return start;
+  }
+}