LESSON 35 / 75·2 min readFoundation

Arrays and strings in Java

Should knowConcept lesson

Key operations

index access: arr[i]
length: arr.length
loops: for, while
string manipulation: substring, charAt, split, equals

Common Java questions

Two Sum
Best Time to Buy and Sell Stock
Maximum Subarray
Move Zeroes
Product of Array Except Self
Longest Substring Without Repeating Characters
Valid Palindrome
Group Anagrams

Java example: two sum

import java.util.*;

class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();

        for (int i = 0; i < nums.length; i++) {
            int needed = target - nums[i];
            if (map.containsKey(needed)) {
                return new int[] { map.get(needed), i };
            }
            map.put(nums[i], i);
        }
        return new int[] {};
    }
}