anujparikh / arrays

Arrays Data Structure

Introduction

An array is collection of items stored at contiguous memory locations. The idea is to store multiple items of same type together. This makes it easier to calculate the position of each element by simply adding an offset to a base value

Advantages of Arrays

• Arrays allow random access of elements. This makes accessing elements by position faster
• You can read or write a list item by referring to its index in constant time
• Arrays have better cache locality that can make a pretty big difference in performance

Best use-case

• Excessive read, as time complexity of read is always O(1)
• Random access to element using index

Time Complexity for Array (average and worst-case)

• Access: O(1)
• Search: O(n)
• Insertion: O(n)
• Deletion: O(n)

Time Complexity for ArrayList java class (worst-case)

• add(int i, E element): O(n - i)
• remove(int i): O(n - i)
• removeRange(int i, int j): O(n - i)
• remove(Object o): O(n)
• contains(Object o): O(n)
• indexOf(Object o): O(n)
• lastIndexOf(Object o): O(n)

Methods in java.util.Array Class

Methods	Description	Returns	Notes
asList	This method returns a fixed-size list backed by the specified array	List
binarySearch	Searches the specified array for the specified value using the binary search algorithm	int	-1 if not found otherwise 0 or more index number
copyOf	Copies the specified array, truncating or padding with defaults (if necessary) so the copy has the specified length	[]
copyOfRange	Copies the specified range of the specified array into a new array	[]
deepEquals	Returns true if the two specified arrays are deeply equal to one another	Boolean
equals	Returns true if the two specified arrays of objects are equal to one another	Boolean
fill	Assigns the specified value to each element of the specified range of the specified array	void
sort	Sorts the specified array into ascending numerical order	void

Common syntaxs

• Initializing Arrays in java

int[] i = new int[4];
int[] i = new int[]{1,2,3,4};

• Copy Arrays in java

Arrays.copyOf(originalArray, lengthOfArray);
Arrays.copyOfRange(originalArray, fromIndex, toIndex);
Arrays.asList(/* pass objects as list */);

Examples

• Remove Duplicates from Sorted Array: Solution (Easy)
• Best Time to Buy and Sell Stock II: Solution (Easy)
• Rotate Array Solution (Easy)
• Contains Duplicate Solution (Easy)
• Single Number Solution (Easy)
• Intersection of 2 Arrays Solution (Easy)
• Plus One Solution (Easy)
• Move Zeros Solution (Easy)
• Two Sum Solution (Easy)
• Valid Sudoku Solution (Easy)
• Rotate Image Solution (Medium)
• 3 Sum Solution (Medium)
• Set Matrix Zeros Solution (Medium)
• Group Anagrams Solution (Medium)
• Increasing Triplet Subsequence Solution (Medium)
• Merge Two Sorted Arrays Solution (Easy)
• First Bad Version Solution (Easy)
• FizzBuzz Solution (Easy)
• Count Prime Solution (Easy)
• Is Power of Three Solution (Easy)
• Pascal's Triangle Solution (Easy)
• Missing Number Solution (Easy)
• Search Insert Position Solution (Easy)
• Sort Colors Solution (Medium)
• Top K Frequent Elements Solution (Medium)
• Kth Largest Elements Solution (Medium)
• Find Peak Element Solution (Medium)
• Find First and Last Position of Element in Sorted Array Solution with O(n) (Medium) - Pending O(log n) solution
• Merge IntervalsSolution (Medium)
• Non-overlapping IntervalsSolution (Medium) (Greedy Algorithm - Need to understand that)