Two Sum

Description:

Solution:

1. Using brute-force
2. Using BST to find complement ⇒ O(nlogn)

e

Add 2 Nums (linked list)

Description:

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Solution:

• We keep going until list 1 and list 2 are both null and carry ≠ 0
• if list 1 ≠ null ⇒ val_list1 = list1.val , if not, val_list1= 0
• if list 2 ≠ null ⇒ val_list2 = list2.val , if not, val_list2= 0
• sum = val_list1 + val_list2 + carry ;
• create new node which value = sum %10
• carry = sum/10
• return the head of new list .next

1. Longest Substring Without Repeating Characters

Description:

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

Solution:

• Using List
• Keep checking sub string whenever encounter duplicate

Longest Palindromic Substring (DP, 2 pointers) - not done

Description:

Given a string s, return the longest palindromic substring in s.

Solution:

1. Using 2 pointers

e

Reverse Integer

Description:

Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231, 231 - 1], then return 0.

Assume the environment does not allow you to store 64-bit integers (signed or unsigned).

Solution:

1. Using String to reverse (only if test case input is small)
2. Using math

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