String – Interview Questions and Practice Problems

A string is traditionally a sequence of characters, either as a literal constant or as some kind of variable. The latter may allow its elements to be mutated and the length changed, or it may be fixed (after creation).

A string is generally understood as a data type and is often implemented as an array of bytes (or words) that stores a sequence of elements, typically characters. String datatypes have historically allocated one byte per character. In C, the length of a string can be stored implicitly by using a special terminating character; often this is the null character (NUL), which has all bits zero.

 
Following is the list of commonly asked string interview questions:

1. Check if a string is a rotated palindrome or notMedium
2. Longest Palindromic Substring ProblemMedium
3. Check if a repeated subsequence is present in a string or notHard
4. Check if strings can be derived from each other by circularly rotating themEasy
5. Check if a set of moves is circular or notMedium
6. Convert a number into a corresponding excel column nameMedium
7. Determine whether two strings are anagram or notEasy
8. Find all interleaving of given stringsEasy
9. Isomorphic StringsMedium
10. Find all possible palindromic substrings of a stringHard
11. Find all possible combinations of words formed from the mobile keypadHard
12. Find all possible combinations by replacing given digits with characters of the corresponding listHard
13. >Find all words that follow the same order of characters as given patternMedium
14. Group anagrams together from a list of wordsMedium
15. Find minimum operations required to transform a string into another stringHard
16. Determine whether a string can be transformed into another string in a single editMedium
17. In-place remove all occurrences of AB and C from a stringEasy
18. Find the longest even-length palindromic sum substring of a stringMedium
19. Print string in the zigzag form in k rowsMedium
20. Run Length Encoding (RLE) Data Compression AlgorithmEasy
21. Find the longest substring of a string containing k distinct charactersHard
22. Find all palindromic permutations of a stringMedium
23. Find all substrings of a string that are a permutation of another stringMedium
24. Find the longest substring of a string containing distinct charactersMedium
25. Find all permutations of a string – C++, Java, PythonHard
26. Iterative approach to finding permutations of a stringHard
27. Find all lexicographically next permutations of a string sorted in ascending orderHard
28. Lexicographically Minimal String RotationMedium
29. Find all strings of a given length containing balanced parenthesesMedium
30. Find all combinations of non-overlapping substrings of a stringMedium
31. Determine whether a string is a palindrome or notEasy
32. Find the minimum number of inversions needed to make an expression balancedMedium
33. Construct the longest palindrome by shuffling or deleting characters from a stringMedium
34. Print all combinations of phrases formed by picking words from each of the given listsMedium
35. Break a string into all possible combinations of non-overlapping substringsMedium
36. Remove all extra spaces from a stringMedium
37. Remove adjacent duplicate characters from a stringEasy
38. Find the first non-repeating character in a string by doing only one traversal of itMedium
39. Find all n-digit strictly increasing numbers (Bottom-up and Top-down approach)Medium
40. Find all n-digit binary numbers having more 1’s than 0’s for any prefixMedium
41. Find all n-digit numbers with a given sum of digitsHard
42. Find all n-digit binary numbers with k-bits set where k ranges from 1 to nHard
43. Find all n-digit binary numbers with an equal sum of bits in their two halvesHard
44. Find all n-digit numbers with equal sum of digits at even and odd indicesHard
45. Find all lexicographic permutations of a stringHard
46. Lexicographic rank of a stringHard
47. Find all lexicographically previous permutations of a string sorted in descending orderHard
48. Replace all non-overlapping occurrences of a patternMedium
49. Find all substrings containing exactly k distinct charactersMedium
50. Introduction to Pattern MatchingBeginner
51. Implementation of KMP AlgorithmHard
52. Reverse a string using recursionEasy
53. Determine whether the characters of a string follow a specified order or notMedium
54. In-place remove all adjacent duplicates from a stringMedium
55. Check if a sentence is syntactically correct or notMedium
56. Number to word conversionHard
57. Implement strstr function in JavaEasy
58. Shortest Superstring ProblemHard
59. Find the shortest route in a device to construct a given stringMedium
60. Find the minimum number possible by doing at-most k swapsMedium
61. Determine whether a string matches with a given patternHard
62. Find all occurrences of the given string in a character matrixHard
63. Difference between Subarray, Subsequence, and SubsetBeginner
64. Check if an expression is balanced or notEasy
65. Find duplicate parenthesis in an expressionMedium
66. Evaluate a postfix expressionEasy
67. Decode a given sequence to construct a minimum number without repeated digitsHard
68. Convert an infix expression into a postfix expressionMedium
69. Reverse a string using a stack data structureEasy
70. Find all binary strings that can be formed from a wildcard patternMedium
71. Find the length of the longest balanced parenthesis in a stringHard
72. Reverse text without reversing individual wordsMedium
73. Reverse a string without using recursionEasy
74. Combinations of words formed by replacing given numbers with corresponding alphabetsHard
75. Longest Common Prefix (LCP) ProblemEasy
76. Longest Common Subsequence ProblemMedium
77. Longest Common Subsequence (LCS) | Space optimized versionMedium
78. Longest Common Subsequence of k–sequencesMedium
79. Longest Common Subsequence | Finding all LCSHard
80. Longest Common Substring ProblemMedium
81. Longest Palindromic Subsequence using Dynamic ProgrammingMedium
82. Longest Repeated Subsequence ProblemMedium
83. Implement Diff UtilityMedium
84. Shortest Common Supersequence ProblemMedium
85. Shortest Common Supersequence | Finding all SCSHard
86. Shortest Common Supersequence Problem using LCSHard
87. The Levenshtein distance (Edit distance) ProblemMedium
88. Count the number of times a pattern appears in a given string as a subsequenceHard
89. Word Break Problem – Dynamic ProgrammingHard
90. Check if a string is k–palindrome or notHard
91. Wildcard Pattern MatchingHard
92. Find the minimum number of deletions required to convert a string into a palindromeMedium
93. Find minimum cuts needed for the palindromic partition of a stringHard
94. Check if a string matches with the given wildcard patternHard
95. Check if a string is interleaving of two other given stringsMedium
96. Find correct order of alphabets in a given dictionary of ancient originHard
97. Find first k non-repeating characters in a string in a single traversalMedium
98. Check if a linked list of strings is palindromicEasy
99. Generate binary numbers between 1 to n using a queueEasy
100. Longest Common Prefix in a given set of strings (using Trie)Medium
101. Lexicographic sorting of a given set of keysMedium
102. Find the maximum occurring word in a given set of stringsEasy
103. Find first k maximum occurring words in a given set of stringsMedium
104. Word Break Problem – Using Trie Data StructureMedium
105. Find all words matching a pattern in the given dictionaryMedium
106. Find the shortest unique prefix for every word in an arrayMedium