Huahua’s Tech Road

花花酱 LeetCode 2410. Maximum Matching of Players With Trainers

By zxi on September 17, 2022

You are given a 0-indexed integer array players, where players[i] represents the ability of the i^th player. You are also given a 0-indexed integer array trainers, where trainers[j] represents the training capacity of the j^th trainer.

The i^th player can match with the j^th trainer if the player’s ability is less than or equal to the trainer’s training capacity. Additionally, the i^th player can be matched with at most one trainer, and the j^th trainer can be matched with at most one player.

Return the maximum number of matchings between players and trainers that satisfy these conditions.

Example 1:

Input: players = [4,7,9], trainers = [8,2,5,8]
Output: 2
Explanation:
One of the ways we can form two matchings is as follows:
- players[0] can be matched with trainers[0] since 4 <= 8.
- players[1] can be matched with trainers[3] since 7 <= 8.
It can be proven that 2 is the maximum number of matchings that can be formed.

Example 2:

Input: players = [1,1,1], trainers = [10]
Output: 1
Explanation:
The trainer can be matched with any of the 3 players.
Each player can only be matched with one trainer, so the maximum answer is 1.

Constraints:

1 <= players.length, trainers.length <= 10⁵
1 <= players[i], trainers[j] <= 10⁹

Solution: Sort + Two Pointers

Sort players and trainers.

Loop through players, skip trainers until he/she can match the current players.

Time complexity: O(nlogn + mlogm + n + m)
Space complexity: O(1)

C++

// Author: Huahua

class Solution {

public:

int matchPlayersAndTrainers(vector<int>& players, vector<int>& trainers) {

sort(begin(players), end(players));

sort(begin(trainers), end(trainers));

const int n = players.size();

const int m = trainers.size();

int ans = 0;

for (int i = 0, j = 0; i < n && j < m; ++i) {

while (j < m && players[i] > trainers[j]) ++j;

if (j++ == m) break;

++ans;

}

return ans;

}

};

花花酱 LeetCode 2409. Count Days Spent Together

By zxi on September 17, 2022

Alice and Bob are traveling to Rome for separate business meetings.

You are given 4 strings arriveAlice, leaveAlice, arriveBob, and leaveBob. Alice will be in the city from the dates arriveAlice to leaveAlice (inclusive), while Bob will be in the city from the dates arriveBob to leaveBob (inclusive). Each will be a 5-character string in the format "MM-DD", corresponding to the month and day of the date.

Return the total number of days that Alice and Bob are in Rome together.

You can assume that all dates occur in the same calendar year, which is not a leap year. Note that the number of days per month can be represented as: [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31].

Example 1:

Input: arriveAlice = "08-15", leaveAlice = "08-18", arriveBob = "08-16", leaveBob = "08-19"
Output: 3
Explanation: Alice will be in Rome from August 15 to August 18. Bob will be in Rome from August 16 to August 19. They are both in Rome together on August 16th, 17th, and 18th, so the answer is 3.

Example 2:

Input: arriveAlice = "10-01", leaveAlice = "10-31", arriveBob = "11-01", leaveBob = "12-31"
Output: 0
Explanation: There is no day when Alice and Bob are in Rome together, so we return 0.

Constraints:

All dates are provided in the format "MM-DD".
Alice and Bob’s arrival dates are earlier than or equal to their leaving dates.
The given dates are valid dates of a non-leap year.

Solution: Math

Convert date to days of the year.

Time complexity: O(1)
Space complexity: O(1)

C++

// Author: Huahua

class Solution {

public:

int countDaysTogether(string arriveAlice, string leaveAlice, string arriveBob, string leaveBob) {

array<int, 12> days{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

auto getDay = [&](string date) {

int mm = (date[0] - '0') * 10 + (date[1] - '0');

int dd = (date[3] - '0') * 10 + (date[4] - '0');

return accumulate(begin(days), begin(days) + mm - 1, dd);

};

int s = max(getDay(arriveAlice), getDay(arriveBob));

int e = min(getDay(leaveAlice), getDay(leaveBob));

return e >= s ? e - s + 1 : 0;

}

};

花花酱 LeetCode 2399. Check Distances Between Same Letters

By zxi on September 17, 2022

You are given a 0-indexed string s consisting of only lowercase English letters, where each letter in s appears exactly twice. You are also given a 0-indexed integer array distance of length 26.

Each letter in the alphabet is numbered from 0 to 25 (i.e. 'a' -> 0, 'b' -> 1, 'c' -> 2, … , 'z' -> 25).

In a well-spaced string, the number of letters between the two occurrences of the i^th letter is distance[i]. If the i^th letter does not appear in s, then distance[i] can be ignored.

Return true if s is a well-spaced string, otherwise return false.

Example 1:

Input: s = "abaccb", distance = [1,3,0,5,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
Output: true
Explanation:
- 'a' appears at indices 0 and 2 so it satisfies distance[0] = 1.
- 'b' appears at indices 1 and 5 so it satisfies distance[1] = 3.
- 'c' appears at indices 3 and 4 so it satisfies distance[2] = 0.
Note that distance[3] = 5, but since 'd' does not appear in s, it can be ignored.
Return true because s is a well-spaced string.

Example 2:

Input: s = "aa", distance = [1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
Output: false
Explanation:
- 'a' appears at indices 0 and 1 so there are zero letters between them.
Because distance[0] = 1, s is not a well-spaced string.

Constraints:

2 <= s.length <= 52
s consists only of lowercase English letters.
Each letter appears in s exactly twice.
distance.length == 26
0 <= distance[i] <= 50

Solution: Hashtable

Use a hastable to store the index of first occurrence of each letter.

Time complexity: O(n)
Space complexity: O(26)

C++

// Author: Huahua

class Solution {

public:

bool checkDistances(string s, vector<int>& distance) {

vector<int> m(26, -1);

for (int i = 0; i < s.length(); ++i) {

int c = s[i] - 'a';

if (m[c] >= 0 && i - m[c] - 1 != distance[c]) return false;

m[c] = i;

}

return true;

}

};

花花酱 LeetCode 2407. Longest Increasing Subsequence II

By zxi on September 11, 2022

You are given an integer array nums and an integer k.

Find the longest subsequence of nums that meets the following requirements:

The subsequence is strictly increasing and
The difference between adjacent elements in the subsequence is at most k.

Return the length of the longest subsequence that meets the requirements.

A subsequence is an array that can be derived from another array by deleting some or no elements without changing the order of the remaining elements.

Example 1:

Input: nums = [4,2,1,4,3,4,5,8,15], k = 3
Output: 5
Explanation:
The longest subsequence that meets the requirements is [1,3,4,5,8].
The subsequence has a length of 5, so we return 5.
Note that the subsequence [1,3,4,5,8,15] does not meet the requirements because 15 - 8 = 7 is larger than 3.

Example 2:

Input: nums = [7,4,5,1,8,12,4,7], k = 5
Output: 4
Explanation:
The longest subsequence that meets the requirements is [4,5,8,12].
The subsequence has a length of 4, so we return 4.

Example 3:

Input: nums = [1,5], k = 1
Output: 1
Explanation:
The longest subsequence that meets the requirements is [1].
The subsequence has a length of 1, so we return 1.

Constraints:

1 <= nums.length <= 10⁵
1 <= nums[i], k <= 10⁵

Solution: DP + Segment Tree | Max range query

Let dp[i] := length of LIS end with number i.
dp[i] = 1 + max(dp[i-k:i])

Naive dp takes O(n*k) time which will cause TLE.

We can use segment tree to speed up the max range query to log(m), where m is the max value of the array.

Time complexity: O(n*logm)
Space complexity: O(m)

C++

// Author: Huahua

class Solution {

public:

int lengthOfLIS(vector<int>& nums, int k) {

const int n = *max_element(begin(nums), end(nums));

vector<int> dp(2 * (n + 1));

auto query = [&](int l, int r) -> int {

int ans = 0;

for (l += n, r += n; l < r; l >>= 1, r >>= 1) {

if (l & 1) ans = max(ans, dp[l++]);

if (r & 1) ans = max(ans, dp[--r]);

}

return ans;

};

auto update = [&](int i, int val) -> void {

dp[i += n] = val;

while (i > 1) {

i >>= 1;

dp[i] = max(dp[i * 2], dp[i * 2 + 1]);

}

};

int ans = 0;

for (int x : nums) {

int cur = 1 + query(max(1, x - k), x);

update(x, cur);

ans = max(ans, cur);

}

return ans;

}

};

花花酱 LeetCode 2405. Optimal Partition of String

By zxi on September 11, 2022

Given a string s, partition the string into one or more substrings such that the characters in each substring are unique. That is, no letter appears in a single substring more than once.

Return the minimum number of substrings in such a partition.

Note that each character should belong to exactly one substring in a partition.

Example 1:

Input: s = "abacaba"
Output: 4
Explanation:
Two possible partitions are ("a","ba","cab","a") and ("ab","a","ca","ba").
It can be shown that 4 is the minimum number of substrings needed.

Example 2:

Input: s = "ssssss"
Output: 6
Explanation:
The only valid partition is ("s","s","s","s","s","s").

Constraints:

1 <= s.length <= 10⁵
s consists of only English lowercase letters.

Solution: Greedy

Extend the cur string as long as possible unless a duplicate character occurs.

You can use hashtable / array or bitmask to mark whether a character has been seen so far.

Time complexity: O(n)
Space complexity: O(1)

C++

// Author: Huahua

class Solution {

public:

int partitionString(string s) {

unordered_set<char> m;

int ans = 0;

for (char c : s) {

if (m.insert(c).second) continue;

m.clear();

m.insert(c);

++ans;

}

return ans + 1;

}

};

C++

// Author: Huahua

class Solution {

public:

int partitionString(string s) {

vector<int> m(26);

int ans = 0;

for (char c : s) {

if (++m[c - 'a'] == 1) continue;

fill(begin(m), end(m), 0);

m[c - 'a'] = 1;

++ans;

}

return ans + 1;

}

};

C++

// Author: Huahua

class Solution {

public:

int partitionString(string s) {

int mask = 0;

int ans = 0;

for (char c : s) {

if (mask & (1 << (c - 'a'))) {

mask = 0;

++ans;

}

mask |= 1 << (c - 'a');

}

return ans + 1;

}

};

Huahua's Tech Road

花花酱 LeetCode 2410. Maximum Matching of Players With Trainers

Solution: Sort + Two Pointers

C++

花花酱 LeetCode 2409. Count Days Spent Together

Solution: Math

C++

花花酱 LeetCode 2399. Check Distances Between Same Letters

Solution: Hashtable

C++

花花酱 LeetCode 2407. Longest Increasing Subsequence II

Solution: DP + Segment Tree | Max range query

C++

花花酱 LeetCode 2405. Optimal Partition of String

Solution: Greedy

C++

C++

C++