adding updates

src/my_project/interviews/top_150_questions_round_23/ex_14_gas_station.py

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+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+
+class Solution:
+    def canCompleteCircuit(self, gas: List[int], cost: List[int]) -> int:
+        """
+        Find the starting gas station to complete the circuit.
+
+        Key insights:
+        1. If total gas < total cost, impossible to complete circuit
+        2. If we can't reach station j from station i, then we can't reach j 
+           from any station between i and j (they all have negative tank balance)
+        3. If a solution exists, it's guaranteed to be unique
+
+        Strategy: Greedy one-pass
+        - Track total gas surplus/deficit
+        - Track current tank from potential starting point
+        - If tank goes negative, reset start to next station
+
+        Time: O(n), Space: O(1)
+        """
+
+        n = len(gas)
+        total_gas = 0      # Total gas surplus/deficit for entire circuit
+        current_tank = 0   # Current gas in tank from start_station
+        start_station = 0  # Potential starting station
+
+        for i in range(n):
+            # Calculate net gas at this station (gain - cost to next)
+            net_gas = gas[i] - cost[i]
+
+            # Add to both total and current tank
+            total_gas += net_gas
+            current_tank += net_gas
+
+            # If current tank is negative, we can't reach next station from start_station
+            # All stations from start_station to i are invalid starting points
+            # Try starting from the next station (i + 1)
+            if current_tank < 0:
+                start_station = i + 1  # Reset starting point
+                current_tank = 0        # Reset tank
+
+        # If total gas is negative, impossible to complete circuit
+        # Otherwise, start_station is the answer
+        return start_station if total_gas >= 0 else -1

src/my_project/interviews_typescript/top_150_questions_round_23/ex_14_gas_station.ts

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+function canCompleteCircuit(gas: number[], cost: number[]): number {
+    const n = gas.length;
+    let totalGas = 0;
+    let currentTank = 0;
+    let startStation = 0;
+
+    for (let i = 0; i < n; i++) {
+        const netGas = gas[i] - cost[i];
+        totalGas += netGas;
+        currentTank += netGas;
+
+        if (currentTank < 0) {
+            startStation = i + 1;
+            currentTank = 0;
+        }
+    }
+
+    return totalGas >= 0 ? startStation : -1;
+};        

tests/test_150_questions_round_23/test_14_gas_station_round_23.py

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+import unittest
+from src.my_project.interviews.top_150_questions_round_23\
+.ex_14_gas_station import Solution
+
+class GasStationTestCase(unittest.TestCase):
+
+    def test_gas_station_first_case(self):
+        solution = Solution()
+        output = solution.canCompleteCircuit(gas = [1,2,3,4,5], 
+                                             cost = [3,4,5,1,2])
+        target = 3 
+        self.assertEqual(output, target)
+
+    def test_gas_station_second_case(self):
+        solution = Solution()
+        output = solution.canCompleteCircuit(gas = [2,3,4], cost = [3,4,3])
+        target = -1 
+        self.assertEqual(output, target)