Coding Solutions

LeetCode

Two Sum

Array Easy

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

Solution (Python):


def twoSum(nums, target):
    lookup = {}
    for i, num in enumerate(nums):
        if target - num in lookup:
            return [lookup[target - num], i]
        lookup[num] = i

Longest Substring Without Repeating Characters

String Medium

Given a string, find the length of the longest substring without repeating characters.

Solution (Python):


def lengthOfLongestSubstring(s):
    charSet = set()
    left = 0
    result = 0
    for right in range(len(s)):
        while s[right] in charSet:
            charSet.remove(s[left])
            left += 1
        charSet.add(s[right])
        result = max(result, right - left + 1)
    return result

GeeksforGeeks

Reverse a Linked List

Linked List Easy

Given a linked list, reverse it and return the head of the modified list.

Solution (Python):


def reverseList(head):
    prev = None
    curr = head
    while curr:
        next_node = curr.next
        curr.next = prev
        prev = curr
        curr = next_node
    return prev

CF

Codeforces

Two Numbers Sum (Similar to LeetCode Two Sum)

Array Implementation 800

Given an array of integers a and an integer target, find indices of two elements whose sum is target. (Similar to LeetCode Two Sum)

Solution (C++):


#include <iostream>
#include <unordered_map>
#include <vector>
using namespace std;
vector<int> twoSum(vector<int>& a, int target) {
    unordered_map<int,int> mp;
    for(int i=0;i<a.size();++i) {
        if(mp.count(target-a[i]))
            return {mp[target-a[i]], i};
        mp[a[i]] = i;
    }
    return {};
}