String Matching LeetCode Problems: 20 Python Solutions

String Matching problems by difficulty

Problems with a complete Python solution are listed first, then by ascending problem number.

Easy (8)

Easy problems
No.	Problem	Topics
0028	Find the Index of the First Occurrence in a String	Two Pointers, String, String Matching
0459	Repeated Substring Pattern	String, String Matching
0572	Subtree of Another Tree	Tree, Depth-First Search, Binary Tree +2
0796	Rotate String	String, String Matching
1408	String Matching in an Array	Array, String, String Matching
1455	Check If a Word Occurs As a Prefix of Any Word in a Sentence	Two Pointers, String, String Matching
1668	Maximum Repeating Substring	String, Dynamic Programming, String Matching
2185	Counting Words With a Given Prefix	Array, String, String Matching

Medium (5)

Medium problems
No.	Problem	Topics
0686	Repeated String Match	String, String Matching
1023	Camelcase Matching	Trie, Array, Two Pointers +2
1764	Form Array by Concatenating Subarrays of Another Array	Greedy, Array, Two Pointers +1
0616	Add Bold Tag in StringPremium	Trie, Array, Hash Table +2
0758	Bold Words in StringPremium	Trie, Array, Hash Table +2

Hard (7)

Hard problems
No.	Problem	Topics
0214	Shortest Palindrome	String, String Matching, Hash Function +1
1392	Longest Happy Prefix	String, String Matching, Hash Function +1
2301	Match Substring After Replacement	Array, Hash Table, String +1
2430	Maximum Deletions on a String	String, Dynamic Programming, String Matching +2
2851	String Transformation	Math, String, Dynamic Programming +1
1397	Find All Good Strings	String, Dynamic Programming, String Matching
2223	Sum of Scores of Built Strings	String, Binary Search, String Matching +3

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python

Please analyze this context and help me answer the question or solve the problem.

Technical interview · 45 minsolution.pyShared editor · Python 3Longest substring without repeatsMediumGiven a string s, return the length of the longest contiguous substring in which every character is unique.s = "abcabcbb"
→ 31def length_of_longest_substring(s: str) -> int:2 last_seen = {}3 left = best = 04 for right, ch in enumerate(s):5 if ch in last_seen and last_seen[ch] >= left:

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

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GPT-6.1 Terra

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python

Please analyze this context and help me answer the question or solve the problem.

Technical interview · 45 minsolution.pyShared editor · Python 3Longest substring without repeatsMediumGiven a string s, return the length of the longest contiguous substring in which every character is unique.s = "abcabcbb"
→ 31def length_of_longest_substring(s: str) -> int:2 last_seen = {}3 left = best = 04 for right, ch in enumerate(s):5 if ch in last_seen and last_seen[ch] >= left:

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

90%Subscription

python

Please analyze this context and help me answer the question or solve the problem.

Technical interview · 45 minsolution.pyShared editor · Python 3Longest substring without repeatsMediumGiven a string s, return the length of the longest contiguous substring in which every character is unique.s = "abcabcbb"
→ 31def length_of_longest_substring(s: str) -> int:2 last_seen = {}3 left = best = 04 for right, ch in enumerate(s):5 if ch in last_seen and last_seen[ch] >= left:

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

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QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

String Matching LeetCode Problems: All 20,
With Python Solutions

String Matching problems by difficulty

Easy (8)

Medium (5)

Hard (7)

When the String Matching problem arrives live.

Approach

Approach

Approach

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String Matching problems by difficulty

Easy (8)8

Medium (5)5

Hard (7)7

When the String Matching problem arrives live.

Approach

Approach

Approach

Keep exploring

Easy (8)

Medium (5)

Hard (7)