Alien Dictionary

There is a new alien language which uses the latin alphabet. However, the order among letters are unknown to you. You receive a list of non-empty words from the dictionary, where words are sorted lexicographically by the rules of this new language. Derive the order of letters in this language. Example 1 Input: [ "wrt", "wrf", "er", "ett", "rftt" ] Output: "wertf" Example 2 Input: [ "z", "x" ] Output: "zx" Example 3 Input: [ "z", "x", "z" ] Output: "" Explanation The order is invalid, so return "".

by lek tin in "algorithm" access_time 3-min read

Random Pick Index

Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array. Note The array size can be very large. Solution that uses too much extra space will not pass the judge. Example int[] nums = new int[] {1,2,3,3,3}; Solution solution = new Solution(nums); // pick(3) should return either index 2, 3, or 4 randomly.

by lek tin in "algorithm" access_time 1-min read

Intersection of Two Arrays

Given two arrays, write a function to compute their intersection. Example 1 Input: nums1 = [1,2,2,1], nums2 = [2,2] Output: [2] Example 2 Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4] Output: [9,4] Note Each element in the result must be unique. The result can be in any order. Solution Use binary search when one of the lists is very long and the other is short class Solution: def intersection(self, nums1: List[int], nums2: List[int]) -> List[int]: if len(nums1) < len(nums2): return self.

by lek tin in "algorithm" access_time 2-min read

Word Break II

Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possible sentences. Note The same word in the dictionary may be reused multiple times in the segmentation. You may assume the dictionary does not contain duplicate words. Example 1 Input: s = "catsanddog" wordDict = ["cat", "cats", "and", "sand", "dog"] Output: [ "cats and dog", "cat sand dog" ] Example 2 Input: s = "pineapplepenapple" wordDict = ["apple", "pen", "applepen", "pine", "pineapple"] Output: [ "pine apple pen apple", "pineapple pen apple", "pine applepen apple" ] Explanation: Note that you are allowed to reuse a dictionary word.

by lek tin in "algorithm" access_time 2-min read

Install Java on Linux

Install manually Step 1: Download the source package from the oracle repository. If your computer is 64-bit, download the x64 version; if it is 32-bit, download the x86 version. Step 2: Extract from the compressed file and move the package folder to /usr/java. rememeber to run these commands as sudo is not the root user. mv downloads-folder/jdk-<version>-linux-xxx.tar.gz /usr/java tar -xvzf jdk-<version>-linux-xxx.tar.gz rm jdk-<version>-linux-xxx.tar.gz Step 3: Add the java path to the ~/.

by lek tin in "linux" access_time 1-min read

Read N Characters Given Read4

The API: int read4(char *buf) reads 4 characters at a time from a file. The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left in the file. By using the read4 API, implement the function int read(char *buf, int n) that reads n characters from the file. Example 1 Input: buf = "abc", n = 4 Output: "abc" Explanation: The actual number of characters read is 3, which is "abc".

by lek tin in "algorithm" access_time 2-min read

CPP Data Types

https://stackoverflow.com/questions/2550345/whats-the-difference-between-unsigned-long-long-int-in-c-c Type Typical Bit Width Typical Range char 1byte -127 to 127 or 0 to 255 unsigned char 1byte 0 to 255 signed char 1byte -127 to 127 int 4bytes -2147483648 to 2147483647 unsigned int 4bytes 0 to 4294967295 signed int 4bytes -2147483648 to 2147483647 short int 2bytes -32768 to 32767 unsigned short int Range 0 to 65,535 signed short int Range -32768 to 32767 long int 4bytes -2,147,483,648 to 2,147,483,647 signed long int 4bytes same as long int unsigned long int 4bytes 0 to 4,294,967,295 float 4bytes +/- 3.

by lek tin in "data-types" access_time 1-min read

Find the Celebrity

Suppose you are at a party with n people (labeled from 0 to n - 1) and among them, there may exist one celebrity. The definition of a celebrity is that all the other n - 1 people know him/her but he/she does not know any of them. Now you want to find out who the celebrity is or verify that there is not one. The only thing you are allowed to do is to ask questions like: “Hi, A.

by lek tin in "algorithm" access_time 2-min read

Binary Numbers

For a 8-bit number, there are two ways to represent number: unsigned values 0 to 255 signed values range from -128 (-2^8 = 10000000) to 127 (2^8 - 1) signed -128 = 10000000 signed -127 = 10000001 signed -1 = 11111111 signed 0 = 00000000 signed 127 = 01111111 signed 127 + (-127) = 10000001 + 01111111 = 0 If a number is assigned with value that is too big for it to hold, overflowing would happen, 2^32 = 4,294,967,296 is the largest unsigned 32 bit value.

by lek tin in "computing" access_time 1-min read

Arrays in Python

Reverse an array arr = [1, 2, 3, 4, 5, 6, 7, 8] reversedArray = arr[::-1] # [8, 7, 6, 5, 4, 3, 2, 1] arr[3:5] = arr[3:5][::-1] Slices with step s[i:j:k] means “slice of s from i to j with step k”. When i and j are absent, the whole sequence is assumed and thus s[::k] means “every k-th item” in the entire sequence. s = range(20) # output: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19] # 3rd item from s: s[::3] # output: [0, 3, 6, 9, 12, 15, 18] # 3rd item from s[2:]: s[2:] # output: [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19] s[2::3] # output: [2, 5, 8, 11, 14, 17] # 3rd item from s[5:12]: s[5:12] # output: [5, 6, 7, 8, 9, 10, 11] s[5:12:3] # output: [5, 8, 11] # 3rd item from s[:10]: s[:10] # output: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] s[:10:3] # output: [0, 3, 6, 9] Clone a list newArr = oldArr[:]

by lek tin in "programming-language" access_time 2-min read