Problem database last updated: June 20, 2025
23 problems · 7 Easy, 12 Medium, 4 Hard · Ranked #82 of 458
7 Easy
30% · avg 23%
12 Medium
52% · avg 59%
4 Hard
17% · avg 18%
Based on 23 reported problems, American Express interviews are in line with industry averages - 17% Hard vs 18% overall. The majority (52%) of questions are Medium difficulty, which is typical for companies that want to see solid fundamentals without excessive trick questions.
Compared to the industry average, American Express puts unusual emphasis on number-theory (8.7% of problems, 17x the industry average), bit-manipulation (13% of problems, 3.9x the industry average), greedy (17.4% of problems, 2.1x the industry average). If you're short on time, these are the categories to double down on.
The most common topics are array (65.2%), hash-table (26.1%), string (21.7%), greedy (17.4%). Problems below are sorted by frequency, the ones at the top are asked most often.
| Problem | Difficulty | Frequency | Topics | |
|---|---|---|---|---|
Minimum Deletions to Make Character Frequencies Unique A string s is called good if there are no two different characters in s that have the same frequency. | Medium | Very Likely | hash-tablestringgreedy | Solve |
Maximum Equal Frequency Given an array nums of positive integers, return the longest possible length of an array prefix of nums, such that it is possible to remove exactly one element... | Hard | Very Likely | arrayhash-table | Solve |
Equal Sum Arrays With Minimum Number of Operations You are given two arrays of integers nums1 and nums2, possibly of different lengths. The values in the arrays are between 1 and 6, inclusive. | Medium | Very Likely | arrayhash-tablegreedy | Solve |
Find a Value of a Mysterious Function Closest to Target Winston was given the above mysterious function func. He has an integer array arr and an integer target and he wants to find the values l and r that make the va... | Hard | Very Likely | arraybinary-searchbit-manipulation | Solve |
Ugly Number III An ugly number is a positive integer that is divisible by a, b, or c. | Medium | Very Likely | mathbinary-searchcombinatorics | Solve |
Percentage of Letter in String Given a string s and a character letter, return the percentage of characters in s that equal letter rounded down to the nearest whole percent. | Easy | Very Likely | string | Solve |
Maximum XOR After Operations You are given a 0-indexed integer array nums. In one operation, select any non-negative integer x and an index i, then update nums[i] to be equal to nums[i] AND... | Medium | Very Likely | arraymathbit-manipulation | Solve |
Divide an Array Into Subarrays With Minimum Cost I You are given an array of integers nums of length n. | Easy | Very Likely | arraysortingenumeration | Solve |
Maximize the Topmost Element After K Moves You are given a 0-indexed integer array nums representing the contents of a pile, where nums[0] is the topmost element of the pile. | Medium | Very Likely | arraygreedy | Solve |
Divide an Array Into Subarrays With Minimum Cost II You are given a 0-indexed array of integers nums of length n, and two positive integers k and dist. | Hard | Very Likely | arrayhash-tablesliding-window | Solve |
Minimum Number of Operations to Make Array XOR Equal to K You are given a 0-indexed integer array nums and a positive integer k. | Medium | Very Likely | arraybit-manipulation | Solve |
Two Sum Given an array of integers nums and an integer target, return the indices of the two numbers that add up to target. | Easy | Very Likely | arrayhash-map | Solve |
Valid Anagram Given two strings s and t, return true if t is an anagram of s, and false otherwise. | Easy | Likely | hash-tablestringsorting | Solve |
3Sum Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0. | Medium | Likely | arraytwo-pointerssorting | Solve |
Minimum Fuel Cost to Report to the Capital There is a tree (i.e., a connected, undirected graph with no cycles) structure country network consisting of n cities numbered from 0 to n - 1 and exactly n - 1... | Medium | Likely | treedepth-first-searchbreadth-first-search | Solve |
Best Time to Buy and Sell Stock You are given an array prices where prices[i] is the price of a given stock on the ith day. | Easy | Likely | arraydynamic-programming | Solve |
Rotate Array Given an integer array nums, rotate the array to the right by k steps, where k is non-negative. | Medium | Likely | arraymathtwo-pointers | Solve |
Valid Palindrome A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forwa... | Easy | Likely | two-pointersstring | Solve |
Add Digits Given an integer num, repeatedly add all its digits until the result has only one digit, and return it. | Easy | Likely | mathsimulationnumber-theory | Solve |
Trapping Rain Water Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining. | Hard | Likely | arraytwo-pointersdynamic-programming | Solve |
Longest Substring Without Repeating Characters Given a string s, find the length of the longest substring without duplicate characters. | Medium | Likely | hash-tablestringsliding-window | Solve |
Reconstruct a 2-Row Binary Matrix Given the following details of a matrix with n columns and 2 rows : | Medium | Likely | arraygreedymatrix | Solve |
Permutations Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order. | Medium | Likely | arraybacktracking | Solve |
Minimum Deletions to Make Character Frequencies Unique
SolveA string s is called good if there are no two different characters in s that have the same frequency.
Maximum Equal Frequency
SolveGiven an array nums of positive integers, return the longest possible length of an array prefix of nums, such that it is possible to remove exactly one element...
Equal Sum Arrays With Minimum Number of Operations
SolveYou are given two arrays of integers nums1 and nums2, possibly of different lengths. The values in the arrays are between 1 and 6, inclusive.
Find a Value of a Mysterious Function Closest to Target
SolveWinston was given the above mysterious function func. He has an integer array arr and an integer target and he wants to find the values l and r that make the va...
Ugly Number III
SolveAn ugly number is a positive integer that is divisible by a, b, or c.
Percentage of Letter in String
SolveGiven a string s and a character letter, return the percentage of characters in s that equal letter rounded down to the nearest whole percent.
Maximum XOR After Operations
SolveYou are given a 0-indexed integer array nums. In one operation, select any non-negative integer x and an index i, then update nums[i] to be equal to nums[i] AND...
Divide an Array Into Subarrays With Minimum Cost I
SolveYou are given an array of integers nums of length n.
Maximize the Topmost Element After K Moves
SolveYou are given a 0-indexed integer array nums representing the contents of a pile, where nums[0] is the topmost element of the pile.
Divide an Array Into Subarrays With Minimum Cost II
SolveYou are given a 0-indexed array of integers nums of length n, and two positive integers k and dist.
Minimum Number of Operations to Make Array XOR Equal to K
SolveYou are given a 0-indexed integer array nums and a positive integer k.
Two Sum
SolveGiven an array of integers nums and an integer target, return the indices of the two numbers that add up to target.
Valid Anagram
SolveGiven two strings s and t, return true if t is an anagram of s, and false otherwise.
3Sum
SolveGiven an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.
Minimum Fuel Cost to Report to the Capital
SolveThere is a tree (i.e., a connected, undirected graph with no cycles) structure country network consisting of n cities numbered from 0 to n - 1 and exactly n - 1...
Best Time to Buy and Sell Stock
SolveYou are given an array prices where prices[i] is the price of a given stock on the ith day.
Rotate Array
SolveGiven an integer array nums, rotate the array to the right by k steps, where k is non-negative.
Valid Palindrome
SolveA phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forwa...
Add Digits
SolveGiven an integer num, repeatedly add all its digits until the result has only one digit, and return it.
Trapping Rain Water
SolveGiven n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.
Longest Substring Without Repeating Characters
SolveGiven a string s, find the length of the longest substring without duplicate characters.
Reconstruct a 2-Row Binary Matrix
SolveGiven the following details of a matrix with n columns and 2 rows :
Permutations
SolveGiven an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.
Frequency scores are based on crowdsourced interview reports. A higher score means the problem has been reported more often in recent American Express interviews.
Very Likely
75-100%
Likely
50-74%
Sometimes
25-49%
Rare
0-24%
American Express interviews focus heavily on array, hash-table, string problems. If you're short on time, these are the categories to prioritize. The problems on this page are sorted by frequency, so start from the top and work your way down.
Beyond solving problems, practice explaining your approach. American Express interviewers care about your thought process - how you break down a problem, consider edge cases, and evaluate tradeoffs between solutions. A clean O(n) solution you can explain clearly beats an O(log n) solution you can't articulate.
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American Express has been reported to ask 23 distinct coding problems. The most common topics are array, hash-table, string. 7 are Easy difficulty, 12 are Medium, and 4 are Hard. Problems are sorted by frequency - the ones at the top are asked most often.
Based on 23 reported problems, American Express interviews are in line with industry averages - 17% Hard vs 18% overall. 52% of questions are Medium difficulty. Focus on the high-frequency Medium problems first, then work through the Hard ones.
Start with the highest-frequency problems listed on this page. Focus on the core topics: array, hash-table, string. Practice solving them under time pressure and explaining your approach out loud. Mock interviews with AI can simulate the real experience.
Simulate a real American Express coding interview with an AI interviewer. Get a scorecard with specific feedback on your problem-solving, code quality, and communication.
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