740. Delete and Earn

[DrDread746]

740. Delete and Earn.cpp

Intuition

The problem is similar to the "House Robber" problem but applied to numbers: if you take a number x, you cannot take x-1 or x+1.
The key insight is to transform the input array into a frequency array f[i], where f[i] counts how many times i appears. Now, instead of worrying about positions in the array, we only care about values. The maximum points we can earn for value i is f[i] * i, and we can use dynamic programming to decide whether to "take" or "skip" each number.

Approach

Build frequency array:
Count how many times each number appears in nums.
Keep track of the maximum number (maxVal) to limit DP size.

Dynamic Programming:
Let dp[i] be the maximum points we can earn considering numbers from 1 to i.
For each i ≥ 2, we have two options:
Skip i: dp[i] = dp[i-1]
Take i: dp[i] = dp[i-2] + f[i] * i (we skip i-1 because taking i deletes i-1)
Base case: dp[1] = f[1]

Return result:
dp[maxVal] is the maximum points we can earn.

Code Solution (C++)

class Solution {
public:
int deleteAndEarn(vector& nums) {
int m = 10001;
int n = nums.size();
int maxVal = 0;
vector f(m, 0);
vector dp(m + 1, 0);

    for (int i = 0; i < n; i++) {
        f[nums[i]]++;
        maxVal = max(maxVal, nums[i]);
    }

    dp[1] = f[1];
    for (int i = 2; i <= maxVal; i++) {
        dp[i] = max(dp[i - 1], dp[i - 2] + f[i] * i);
    }

    return dp[maxVal];
}

};

Related Issues

Closes #254

By submitting this PR, I confirm that:

• [✅] This is my original work not totally AI generated
• [✅] I have tested the solution thoroughly on leetcode
• [✅] I have maintained proper PR description format
• [✅] This is a meaningful contribution, not spam

Summary by Sourcery

Add C++ solutions for LeetCode problems 3297, 3298, and 740

New Features:

• Implement sliding window solutions for LeetCode 3297 and 3298 to count substrings of word1 that can be rearranged to contain word2
• Implement frequency-based dynamic programming solution for LeetCode 740 (Delete and Earn)

[sourcery-ai]

Reviewer's Guide

This PR adds C++ solutions for three LeetCode problems: sliding window approach for substring counting (problems 3297 and 3298) and a dynamic programming solution for "Delete and Earn" (problem 740), transforming the latter into a frequency-based DP.

Class diagram for new Solution classes added

classDiagram
class Solution_3297 {
  +long long validSubstringCount(string word1, string word2)
}
class Solution_3298 {
  +long long validSubstringCount(string word1, string word2)
}
class Solution_740 {
  +int deleteAndEarn(vector<int>& nums)
}
Solution_3297 : validSubstringCount(word1, word2)
Solution_3298 : validSubstringCount(word1, word2)
Solution_740 : deleteAndEarn(nums)

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Flow diagram for the dynamic programming approach in Delete and Earn (Problem 740)

flowchart TD
    A["Build frequency array f[i] from nums"] --> B["Find maxVal in nums"]
    B --> C["Initialize dp[1] = f[1]"]
    C --> D["For i = 2 to maxVal"]
    D --> E["dp[i] = max(dp[i-1], dp[i-2] + f[i]*i)"]
    E --> F["Return dp[maxVal]"]

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File-Level Changes

Change	Details	Files
Added sliding window algorithm for counting valid substrings	Initialized frequency arrays for target pattern and current window Used two-pointer expansion and contraction to maintain match count Accumulated results by counting valid suffixes when full match is detected	3297. Count Substrings That Can Be Rearranged to Contain a String I.cpp 3298. Count Substrings That Can Be Rearranged to Contain a String II.cpp
Implemented dynamic programming solution for 'Delete and Earn' by converting inputs into a frequency-based problem	Built frequency array f and tracked maxVal from input nums Initialized dp array with base case dp[1] Computed dp[i] = max(dp[i-1], dp[i-2] + f[i] * i) iteratively Returned dp[maxVal] as the maximum points	740. Delete and Earn.cpp

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#254	Provide a working C++ solution for LeetCode problem 740 (Delete and Earn) following the described dynamic programming approach.	✅
#254	Include an Approach and Intuition section explaining the solution in the PR description.	✅
#254	Ensure the filename follows the convention '[Number]. [Problem Title].cpp'.	✅

Possibly linked issues

• #740: The PR adds the exact C++ solution described in issue 740 for the 'Delete and Earn' problem.

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