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How to Solve Count Different Palindromic Subsequences Problem
Master the Count Different Palindromic Subsequences LeetCode problem with undetectable real-time assistance. Get instant solutions and explanations during your coding interviews.
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LeetCode ProblemCount Different Palindromic Subsequences
Given a string s, return the number of different non-empty palindromic subsequences in s. Since the answer may be very large, return it modulo 109 + 7. A subsequence of a string is obtained by deleting zero or more characters from the string. A sequence is palindromic if it is equal to the sequence reversed. Two sequences a1, a2, ... and b1, b2, ... are different if there is some i for which ai != bi.
StringDynamic Programming
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Problem Breakdown
Understanding the Count Different Palindromic Subsequences Problem
Let's break down this LeetCode problem and understand what makes it challenging in interview settings.
Problem Statement
Given a string s, return the number of different non-empty palindromic subsequences in s. Since the answer may be very large, return it modulo 109 + 7. A subsequence of a string is obtained by deleting zero or more characters from the string. A sequence is palindromic if it is equal to the sequence reversed. Two sequences a1, a2, ... and b1, b2, ... are different if there is some i for which ai != bi.
HardProblem #730
LeetCodeCount Different Palindromic Subsequences
Related Topics
StringDynamic Programming
How Phantom Code Helps
Get real-time assistance for Count Different Palindromic Subsequences problems during coding interviews. Phantom Code provides instant solutions and explanations.
Examples
# Example 1
Input
s = "bccb"
Output
6
# Example 2
Input
s = "abcdabcdabcdabcdabcdabcdabcdabcddcbadcbadcbadcbadcbadcbadcbadcba"
Output
104860361
Constraints
1 <= s.length <= 1000
s[i] is either 'a', 'b', 'c', or 'd'.
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Solve Count Different Palindromic Subsequences — Given a string s, return the number of different non-empty palindromic subsequen...
Here's the optimal approach using String:
def solve(input):
# Optimal O(n) solution
return result
Time: O(n) | Space: O(n)
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Frequently Asked Questions
Common questions about solving Count Different Palindromic Subsequences and using Phantom Code during coding interviews.
How does Phantom Code help me solve coding problems like Count Different Palindromic Subsequences during interviews?
Phantom Code generates complete solutions instantly with proper complexity analysis, letting you focus on explaining your approach and demonstrating problem-solving skills rather than getting stuck on implementation details during high-pressure situations.
What if the interviewer asks follow-up questions or modifications to problems like Count Different Palindromic Subsequences?
Phantom Code adapts in real-time. Screenshot the modified problem or use audio mode to capture the interviewer's follow-up, and get an updated solution within seconds — including edge cases and optimizations.
Can Phantom Code help me communicate my solution for problems like Count Different Palindromic Subsequences?
Yes. Phantom Code provides step-by-step approach explanations with 3 progressive thoughts, so you can walk through your solution naturally. It also provides time and space complexity analysis to discuss trade-offs.
How does Phantom Code assist with different programming languages for Count Different Palindromic Subsequences type problems?
Phantom Code supports 11 programming languages including Python, Java, C++, JavaScript, TypeScript, Go, Rust, Ruby, Swift, Kotlin, and C#. Set your preferred language and get idiomatic solutions.
What coding mistakes does Phantom Code help me avoid during Count Different Palindromic Subsequences interviews?
Phantom Code catches common mistakes like off-by-one errors, missing edge cases, incorrect base conditions, and suboptimal approaches. It provides clean, well-structured code that handles all edge cases.
Is Phantom Code detectable when solving problems like Count Different Palindromic Subsequences during live interviews?
No. Phantom Code runs as an invisible desktop overlay that doesn't appear in screen shares, recordings, or proctoring software. It works with Zoom, HackerRank, CodeSignal, CoderPad, and all major platforms.
How does Phantom Code help when I'm struggling with Count Different Palindromic Subsequences style questions under pressure?
The AI provides structured guidance: first the approach (what algorithm/data structure to use and why), then the implementation with clean code, and finally complexity analysis. This helps you think clearly even under pressure.
Does Phantom Code work for the coding platforms used in Count Different Palindromic Subsequences interviews?
Yes. Phantom Code works with all major coding platforms including LeetCode, HackerRank, CodeSignal, CoderPad, HackerEarth, and any browser-based coding environment.
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