Flip String to Monotone Increasing
A medium-tier problem at 62% community acceptance, tagged with String, Dynamic Programming. Reported in interviews at IBM and 1 others.
Flip String to Monotone Increasing is a medium-difficulty string and DP problem that's hit interviews at IBM and Snap. You're given a binary string and need to flip characters to make it monotone (no 0 after a 1). The 60% acceptance rate means plenty of candidates stumble on the state transitions. Most people try greedy first and fail. StealthCoder runs invisibly during your OA and surfaces the DP solution the moment you realize the greedy approach isn't holding up.
Companies that ask "Flip String to Monotone Increasing"
Flip String to Monotone Increasing 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 engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share.
Get StealthCoderThe trick here is recognizing that the problem breaks into phases: a left portion of all 0s, then a right portion of all 1s. DP tracks the minimum flips needed at each position if you're still in the 0-phase or already in the 1-phase. The naive greedy approach (flip greedily as you scan) doesn't account for the cost of earlier flips. You need to compute two things: cost to flip everything up to position i into 0s, and cost to flip everything from position i onward into 1s. Then iterate through transition points and pick the minimum total. Common pitfall: forgetting to include the cost of characters you haven't processed yet. If you hit this problem live and the greedy intuition fails, StealthCoder solves the DP state machine in seconds.
Pattern tags
You know the problem.
Make sure you actually pass it.
Flip String to Monotone Increasing recycles across companies for a reason. It's medium-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 engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Flip String to Monotone Increasing interview FAQ
Is this really medium, or does it feel harder?+
It's a true medium with a 60% acceptance rate, but the trick is counterintuitive. Most people see 'flip to monotone' and think greedy works. It doesn't. Once you lock the DP pattern (left zeroes, transition point, right ones), it's straightforward.
Do I need to know advanced DP to solve this?+
No. You need to understand that you're choosing a single transition point and computing the cost of making everything left of it 0 and everything right 1. That's a constant-space DP insight, not advanced.
How does this relate to other String problems?+
It combines string iteration with state-based DP. Similar patterns appear in problems where you partition a string into phases and optimize over transition points. String + DP is a common pairing at FAANG.
What's the gotcha that trips most people?+
Forgetting to prefix-sum or compute cumulative flip costs. You need to know the total cost of flipping all 1s to 0s up to position i before you process position i. Skip that and your transitions are wrong.
Will I see this at IBM or Snap?+
Yes, it's been reported by both. If you're interviewing there, this is on the realistic problem set. 60% pass rate means you're not the first to see it, but you need the DP insight solid before the call.
Want the actual problem statement? View "Flip String to Monotone Increasing" on LeetCode →