add solution of problem 134: gas station

Author: ppulse

GasStation134/README.md

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+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.

GasStation134/Solution.java

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+public class Solution {
+    public int canCompleteCircuit(int[] gas, int[] cost) {
+        if (gas == null || cost == null || gas.length != cost.length)
+            return -1;
+        
+        int[] gasLeft = new int[gas.length];
+
+        for (int i = 0; i < gas.length;) {
+            int j = 0;
+            if (gas[i] >= cost[i]) {
+                int remainGas = 0;
+                for (; j < gas.length && remainGas >= 0; j++)  {
+                    int idx = (i + j) % gas.length;
+                    remainGas += gas[idx] - cost[idx];
+                }
+                if (j == gas.length && remainGas >= 0)
+                    return i;
+            }
+            
+            if (j > 0)
+                i += j;
+            else
+                i++;
+        }
+        
+        return -1;
+    }
+}