Positions of Large Groups - Problem
Imagine you're analyzing patterns in a string of characters! Given a string s of lowercase letters, characters naturally form consecutive groups of the same character.
For example, in the string "abbxxxxzyy", we can identify these groups:
• "a" at position [0,0]
• "bb" at positions [1,2]
• "xxxx" at positions [3,6]
• "z" at position [7,7]
• "yy" at positions [8,9]
A group is considered "large" if it contains 3 or more characters. Your task is to find all large groups and return their [start, end] intervals (inclusive) sorted by start index.
Goal: Return intervals of every large group sorted in increasing order by start index.
Input & Output
example_1.py — Basic Case
$
Input:
s = "abbxxxxzyy"
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Output:
[[3,6]]
💡 Note:
The groups are "a", "bb", "xxxx", "z", "yy". Only "xxxx" has 3+ characters, spanning indices 3 to 6.
example_2.py — Multiple Large Groups
$
Input:
s = "abcdddeeeeaabbbcd"
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Output:
[[3,5],[6,9],[12,14]]
💡 Note:
Large groups are "ddd" at [3,5], "eeee" at [6,9], and "bbb" at [12,14].
example_3.py — No Large Groups
$
Input:
s = "aba"
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Output:
[]
💡 Note:
All groups ("a", "b", "a") have size 1, so no large groups exist.
Constraints
- 1 ≤ s.length ≤ 1000
- s contains only lowercase English letters
- Groups are formed by consecutive identical characters
Visualization
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Understanding the Visualization
1
Scan String
Move through string character by character
2
Track Groups
Keep count of consecutive identical characters
3
Identify Large Groups
Mark groups with 3+ characters
4
Record Positions
Store start and end indices of large groups
Key Takeaway
🎯 Key Insight: Use a single pass with two pointers to efficiently identify consecutive character groups and check their sizes - no need for complex data structures!
💡
Explanation
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