Design a stack that supports push, pop, top, and retrieving the minimum element in constant time. push(x) — Push element x onto stack. pop() — Removes the element on top of the stack. top() — Get the top element. getMin() — Retrieve the minimum element in the stack. Java Solution To make constant time of … Read more
A peak element is an element that is greater than its neighbors. Given an input array where num[i] ≠num[i+1], find a peak element and return its index. The array may contain multiple peaks, in that case return the index to any one of the peaks is fine. You may imagine that num[-1] = num[n] … Read more
Given an array A of non-negative integers, the array is squareful if for every pair of adjacent elements, their sum is a perfect square. Return the number of permutations of A that are squareful. Two permutations A1 and A2 differ if and only if there is some index i such that A1[i] != A2[i]. Example … Read more
Given a double linked list’s head node, reverse the list and return the new head node. Java Solution /* * For your reference: * * DoublyLinkedListNode { * int data; * DoublyLinkedListNode next; * DoublyLinkedListNode prev; * } * */ static DoublyLinkedListNode reverse(DoublyLinkedListNode head) { DoublyLinkedListNode p = head; DoublyLinkedListNode newHead = head; while(p!=null){ … Read more
Suppose a sorted array is rotated at some pivot unknown to you beforehand. (i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2). Find the minimum element.You may assume no duplicate exists in the array. Analysis This problem is a binary search and the key is breaking the … Read more
Reading data from csv files is very useful as csv file is a standard output of many programs. In R, you can read csv file in one line: df <- read.csv("/path/to/file.txt", row.names=1,head=FALSE, sep=",")df <- read.csv("/path/to/file.txt", row.names=1,head=FALSE, sep=",") The code above specifies the first column is just a name by using row.names=1. By using head=FALSE, it … Read more
The following code can read data from MySQL database. import MySQLdb # Open database connection db = MySQLdb.connect("localhost","username","password","DBName") # prepare a cursor object using cursor method cursor = db.cursor() sql = "select * from table1" cursor.execute(sql) results = cursor.fetchall() for row in results: print row[0] # disconnect from server db.close()import MySQLdb … Read more
How to read a text file line by line using Python? Reading files in python is extremely simple to do. The following is the code: with open("/path/to/file.txt") as f: for line in f: linedata = line.split(’\t’)with open("/path/to/file.txt") as f: for line in f: linedata = line.split(‘\t’) Very often, you may want to split each line … Read more
The following code records how I load csv files to R and run hierarchical clustering algorithm on the data. I have to say that using R to plot the data is extremely EASY to do! > df <- read.csv("C:/Users/Creek/Desktop/data.txt", row.names=1,head=FALSE, sep=",") > d <- dist(as.matrix(df)) > hc <- hclust(d) > plot(hc) > q()> df <- … Read more
Given an array of integers and an integer k, find the total number of continuous subarrays whose sum equals to k. Example 1: Input:nums = [1,1,1], k = 2 Output: 2 Note that empty array is not considered as a subarray. Java Solution The sum problems can often be solved by using a hash map … Read more
Given an array of integers find the maximum and minimum elements by using minimum comparisons.
Given an array of integers nums and a positive integer k, find whether it’s possible to divide this array into k non-empty subsets whose sums are all equal. Example 1: Input: nums = [4, 3, 2, 3, 5, 2, 1], k = 4 Output: True Explanation: It’s possible to divide it into 4 subsets (5), … Read more