2021/winter interview training for facebook/google

puzzles/training/gas_station.cpp

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+/*
+
+Gas Station
+
+    Asked in:
+    Bloomberg
+    Google
+    DE Shaw
+    Amazon
+    Flipkart
+
+Given two integer arrays A and B of size N.
+There are N gas stations along a circular route, where the amount of gas at station i is A[i].
+
+You have a car with an unlimited gas tank and it costs B[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 minimum starting gas station’s index if you can travel around the circuit once, otherwise return -1.
+
+You can only travel in one direction. i to i+1, i+2, … n-1, 0, 1, 2.. Completing the circuit means starting at i and
+ending up at i again.
+
+
+
+Input Format
+
+The first argument given is the integer array A.
+The second argument given is the integer array B.
+
+Output Format
+
+Return the minimum starting gas station's index if you can travel around the circuit once, otherwise return -1.
+
+For Example
+
+Input 1:
+    A =  [1, 2]
+    B =  [2, 1]
+Output 1:
+    1
+    Explanation 1:
+        If you start from index 0, you can fill in A[0] = 1 amount of gas. Now your tank has 1 unit of gas. But you need B[0] = 2 gas to travel to station 1.
+        If you start from index 1, you can fill in A[1] = 2 amount of gas. Now your tank has
+*/
+int Solution::canCompleteCircuit(const vector<int> &A, const vector<int> &B) {
+    int f = 0;
+    int mf = 0;
+    size_t mi = -1;
+    for (size_t i =0; i < A.size(); ++i){
+        f += A[i]-B[i];
+        if (f < mf){
+            mf = f;
+            mi = i;
+        }
+        if ((i+1) == A.size() && f < 0){
+            return -1;
+        }
+    }
+
+    return (mi+1) % A.size();
+}