In array, there are frequently asked questions “Two sum”, “three sum”, “find subarray with given sum”. Here is a target sum problem with a twist – find a number not in the array, but can make subarray sum equals to or close to the target. To solve “Find a number …
To find number of possible combinations of valid parentheses, we have to know Catalan number. Catalan numbers are a sequence of natural numbers that follow the formula showing below. The first few Catalan numbers for n = 0, 1, 2, 3, 4, 5 … Cn = 1, 1, 2, 5, …
Given a set of numbers, there are many different ways to add operators and parentheses to form an valid expression. The operations are +, -, *, /. The operator * and / have higher precedence than + and – . In infix expressions, we add parentheses to override the normal …
Permutation of multiple arrays and iterator has two tasks. First is the permutation of multiple arrays and output as an array of new combinations. The second is to implement the iterator of this new array. Permutation is an important topic in the fields of combinatorics. It is usually implemented using …
Royal succession order is also known as the line of succession to the British throne. Under common law, the crown is inherited by a sovereign’s children or by a childless sovereign’s nearest collateral line. You can get the current British monarchy succession order here. As programmer, you might be asked …
Similar to convert JSON file to objects, we can covert hierarchical list to a nested object. The input is like a table of content with multiple levels, the output is a nested object obj.children[1].children[2]. “obj” is the top level object. Each nested object’s level maps with the level in the …
Given an array of sets, find the least common set. The least common set is also an outlier set, that has least in common with other sets. There are different ways to find the least common set. One ways is to use union-find to make all elements in a disjoint …
Comparator is used to sort the objects by different attributes. You can simply put lambda in the place where requires Comparator. Lambda is preferred when the comparison is simple. Here are the syntax and examples in Java, JavaScript and Python. Sometime you may have complex comparisons involving multiple attributes. For example, …
Java Comparators are used to sort the user defined objects. It gives you flexibility to sort the objects in multiple ways. For example you can sort strings by alphabetical order, or by their lengths. If you have a People class with first name, last name and age, you can sort …
In HashMap, the key can be any data type. The most common used data types are String and Integer. When you use custom defined object as key, you have to specify how to order them. In Java, you use TreeMap. In JavaScript and Python, you use lambda expressions.
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import java.util.Map; import java.util.TreeMap; class Fruit implements Comparable<Fruit>{ private String name; private double price; private String origin; public Fruit(String itm, double pr, String loc){ this.name = itm; this.price = pr; this.origin = loc; } public int compareTo(Fruit y){ return (int)(price-y.price); } public String toString(){ return name+ " " + price + " " + origin; } } public class HashMapObjectAsKey { public static void main(String a[]){ Map<Fruit, String> hm = new TreeMap<Fruit, String>(); hm.put(new Fruit("Banana", 20.13, "Hawaii"), "Mayflower"); hm.put(new Fruit("Apple", 40.09, "Japan"), "Queen Mary"); hm.put(new Fruit("Orange", 15.7, "Florida"), "Victory"); hm.put(new Fruit("Orange", 23.7, "California"), "Black Pearl"); //sort by key, Time O(nlog), Space O(n), n is number of fruits in map Map<Fruit, String> res = new TreeMap<Fruit, String>(hm); for (Fruit h: res.keySet()) { System.out.println(h + " -" + hm.get(h)); } } } |
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class Fruit { constructor(itm, pr, loc){ this.name = itm; this.price = pr; this.origin = loc; } toString() { return this.name + " " + this.price + " " + this.origin; } } const fruit1 = new Fruit("Banana", 20.13, "Hawaii"); const fruit2 = new Fruit("Apple", 40.09, "Japan"); const fruit3 = new Fruit("Orange", 15.7, "Florida"); const fruit4 =new Fruit("Mango", 23.7, "Philippines"); //object as key const fruitAsKey = new Map(); fruitAsKey.set(fruit1, "Mayflower"); fruitAsKey.set(fruit2, "Queen Mary"); fruitAsKey.set(fruit3, "Victory"); fruitAsKey.set(fruit4, "Black Pearl"); //sort by key, Time O(nlogn), Space O(n), n is number of fruits in map var res1 = new Map([...fruitAsKey].sort(([k1,v1], [k2,v2])=> { return k1.price - k2.price; })); console.log(res1); |
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