Optimize Travel Costs and Generate Rotational Symmetric Numbers

##### Scenario You are building a travel-search engine that must 1) show customers the cheapest round-trip they can book if departure and return prices vary by day, and 2) generate all k-digit numbers that still look the same after a 180° rotation for fraud-detection image checks. ##### Question Given two arrays, dep[i] = outbound ticket price on day i and ret[j] = return ticket price on day j, design an algorithm that returns the minimum possible total cost for any valid round-trip (depart before return). Analyze time and space complexity and discuss possible optimizations or alternative solutions. Given an integer k, generate all k-digit numbers that remain identical when rotated 180°. Provide an algorithm, analyze its complexity, and explain how your code handles corner cases. ##### Hints Cheapest flight: pre-compute suffix minima or use two-pointer scan. Strobogrammatic: recurse from outer to inner, pairing digits {0,0},{1,1},{6,9},{8,8},{9,6}.