Construct String with Minimum Cost
A hard-tier problem at 19% community acceptance, tagged with Array, String, Dynamic Programming. Reported in interviews at Mitsogo and 0 others.
Construct String with Minimum Cost is a hard DP problem that appears infrequently in assessments, but when it hits your OA, it can derail your session fast. The problem forces you to think backwards: instead of building a string forward, you need to recognize that optimal cost comes from picking the right substrings in the right order. With a 19% acceptance rate, most candidates miss the core insight on first read. If you're prepping for Mitsogo or any company that values DP chops, this problem tests whether you can spot the recurrence relation under pressure. StealthCoder is the net if you freeze on the pattern.
Companies that ask "Construct String with Minimum Cost"
Construct String with Minimum Cost is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code.
Get StealthCoderThe trick here is recognizing this as a DP problem where you track the minimum cost to construct prefixes of your target string. Brute force tries all permutations of the given strings, which explodes immediately. Instead, you iterate through your target string and at each position ask: which of my available strings can I use to extend my current construct, and what's the cheapest way to do it? The recurrence is straightforward once you see it, but the insight that you're optimizing cost over all valid string combinations doesn't come naturally to most. Common pitfalls include building the string forward instead of thinking in terms of prefix costs, or failing to consider all possible decompositions. When you hit this live and the naive approach times out, StealthCoder surfaces the DP transition in seconds, invisible to the proctor.
Pattern tags
You know the problem.
Make sure you actually pass it.
Construct String with Minimum Cost recycles across companies for a reason. It's hard-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Construct String with Minimum Cost interview FAQ
Is this really a hard problem or is the rating inflated?+
The 19% acceptance rate puts it genuinely hard. Most candidates either miss the DP structure entirely or implement it inefficiently. It's not a trick question, but the insight that you need to optimize cost over string combinations doesn't strike without solid DP fundamentals.
How does this relate to other string DP problems?+
It mirrors problems like Word Break and Paint House, where you decompose a larger problem into overlapping subproblems and track cost or feasibility. The difference here is you're explicitly minimizing cost across multiple valid decompositions, not just finding one solution.
What's the main mistake candidates make?+
Trying to greedily pick the cheapest substring at each step, or building the string forward instead of thinking in prefix costs. The optimal solution requires DP to explore all valid orderings and their cumulative costs simultaneously.
Is this still asked at real companies?+
Mitsogo is the only company in recent reports for this problem, suggesting it's not a mainstream FAANG filter. But any company that uses hard DP problems in screening could deploy it. If you see it, you're in a specialized or harder round.
How much time should I spend drilling this before my OA?+
If Suffix Array or extreme DP is on your target company's list, yes. Otherwise, understand the DP pattern and move on. At 19% acceptance, it's a tiebreaker question, not a must-pass. Focus on medium DP first.
Want the actual problem statement? View "Construct String with Minimum Cost" on LeetCode →