Arrays and strings in Java
Practice this questionWANT TO UNDERSTAND THE CONCEPT FIRST?Learn Arrays and strings in Java
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[] {};
}
}Time and space complexity
- Time: O(n)
- Space: O(n)
Adapted from 15_DSA_JAVA.md · “2. Arrays and strings in Java”. Code examples are study fragments. Difficulty and core labels are editorial estimates; version-specific behavior should be checked against your project.