Leetcode

Given two strings s and t of length N, find the maximum number of possible matching pairs in strings s and t after swapping exactly two characters within s. A swap is switching s[i] and s[j], where s[i] and s[j] denotes the character that is present at the ith and jth index of s, respectively. The matching pairs of the two strings are defined as the number of indices for which s[i] and t[i] are equal. Note: This means you must swap two characters at different indices. Signature int matchingPairs(String s, String t) Input ...

Pair Sums Given a list of n integers arr[0..(n-1)], determine the number of different pairs of elements within it which sum to k. If an integer appears in the list multiple times, each copy is considered to be different; that is, two pairs are considered different if one pair includes at least one array index which the other doesn’t, even if they include the same values. Signature int numberOfWays(int[] arr, int k) Input n is in the range [1, 100,000]. Each value arr[i] is in the range [1, 1,000,000,000]. k is in the range [1, 1,000,000,000]. Output Return the number of different pairs of elements which sum to k. ...

Given two integer arrays of equal length target and arr. In one step, you can select any non-empty sub-array of arr and reverse it. You are allowed to make any number of steps. Return True if you can make arr equal to target, or False otherwise. Example 1: Input: target = [1,2,3,4], arr = [2,4,1,3] Output: true Explanation: You can follow the next steps to convert arr to target: 1- Reverse sub-array [2,4,1], arr becomes [1,4,2,3] 2- Reverse sub-array [4,2], arr becomes [1,2,4,3] 3- Reverse sub-array [4,3], arr becomes [1,2,3,4] There are multiple ways to convert arr to target, this is not the only way to do so. Example 2: Input: target = [7], arr = [7] Output: true Explanation: arr is equal to target without any reverses. Example 3: Input: target = [1,12], arr = [12,1] Output: true Example 4: Input: target = [3,7,9], arr = [3,7,11] Output: false Explanation: arr doesn't have value 9 and it can never be converted to target. Example 5: Input: target = [1,1,1,1,1], arr = [1,1,1,1,1] Output: true Constraints: ...

Given a file and assume that you can only read the file using a given method read4, implement a method read to read n characters. Your method read may be called multiple times. Method read4: The API read4 reads four consecutive characters from file, then writes those characters into the buffer array buf4. The return value is the number of actual characters read. ...

Android devices have a special lock screen with a 3 x 3 grid of dots. Users can set an “unlock pattern” by connecting the dots in a specific sequence, forming a series of joined line segments where each segment’s endpoints are two consecutive dots in the sequence. A sequence of k dots is a valid unlock pattern if both of the following are true: All the dots in the sequence are distinct. If the line segment connecting two consecutive dots in the sequence passes through the center of any other dot, the other dot must have previously appeared in the sequence. No jumps through the center non-selected dots are allowed. For example, connecting dots 2 and 9 without dots 5 or 6 appearing beforehand is valid because the line from dot 2 to dot 9 does not pass through the center of either dot 5 or 6. However, connecting dots 1 and 3 without dot 2 appearing beforehand is invalid because the line from dot 1 to dot 3 passes through the center of dot 2. ...

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [-1,0,3,5,9,12], target = 9 Output: 4 Explanation: 9 exists in nums and its index is 4 Example 2: Input: nums = [-1,0,3,5,9,12], target = 2 Output: -1 Explanation: 2 does not exist in nums so return -1 Constraints: ...

You are given an array arr of N integers. For each index i, you are required to determine the number of contiguous subarrays that fulfill the following conditions: The value at index i must be the maximum element in the contiguous subarrays, and These contiguous subarrays must either start from or end on index i. Signature int[] countSubarrays(int[] arr) Input Array arr is a non-empty list of unique integers that range between 1 to 1,000,000,000 Size N is between 1 and 1,000,000 Output An array where each index i contains an integer denoting the maximum number of contiguous subarrays of arr[i] ...

You have a pointer at index 0 in an array of size arrLen. At each step, you can move 1 position to the left, 1 position to the right in the array, or stay in the same place (The pointer should not be placed outside the array at any time). Given two integers steps and arrLen, return the number of ways such that your pointer still at index 0 after exactly steps steps. Since the answer may be too large, return it modulo 109 + 7. ...

Given a URL startUrl and an interface HtmlParser, implement a Multi-threaded web crawler to crawl all links that are under the same hostname as startUrl. Return all URLs obtained by your web crawler in any order. Your crawler should: Start from the page: startUrl Call HtmlParser.getUrls(url) to get all URLs from a webpage of a given URL. Do not crawl the same link twice. Explore only the links that are under the same hostname as startUrl. As shown in the example URL above, the hostname is example.org. For simplicity’s sake, you may assume all URLs use HTTP protocol without any port specified. For example, the URLs http://leetcode.com/problems and http://leetcode.com/contest are under the same hostname, while URLs http://example.org/test and http://example.com/abc are not under the same hostname. ...

Given an integer array sorted in non-decreasing order, there is exactly one integer in the array that occurs more than 25% of the time, return that integer. Example 1: Input: arr = [1,2,2,6,6,6,6,7,10] Output: 6 Example 2: Input: arr = [1,1] Output: 1 Constraints: 1 <= arr.length <= 10^4 0 <= arr[i] <= 10^5 Solution class Solution { public int findSpecialInteger2(int[] arr) { int n = arr.length; int val1 = arr[n / 4]; int val2 = arr[n / 4 * 2] ; int val3 = arr[n / 4 * 3]; int val4 = arr[n - 1]; int count1 = countFreq(arr, val1); int count2 = countFreq(arr, val2); int count3 = countFreq(arr, val3); int count4 = countFreq(arr, val4); if (count1 >= count2 && count1 >= count3 && count1 >= count4) { return val1; } if (count2 >= count1 && count2 >= count3 && count2 >= count4) { return val2; } if (count3 >= count1 && count3 >= count2 && count3 >= count4) { return val3; } return val4; } int countFreq(int[] arr, int val) { int mid = Arrays.binarySearch(arr, val); int right = mid; while (right < arr.length - 1 && arr[right] == arr[right + 1]) { right++; } int left = mid; while (left > 0 && arr[left] == arr[left - 1]) { left--; } return right - left; } } Solution 2 class Solution { public int findSpecialInteger(int[] arr) { int n = arr.length; int t = n / 4; for (int i = 0; i < n - t; i++) { if (arr[i] == arr[i + t]) { return arr[i]; } } return -1; } }