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LeetCode 5. Valid Parentheses [Strings, Stack] Problem: Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Note that an empty string is also considered valid. Example 1: Input: "()" Output: true Example 2: Input: "()[]{}" Output: true Exa.. 2020. 6. 12.
LeetCode. House Robber [Dynamic Programming] Problem: You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses have security system connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given a list of non-negative integers representing t.. 2020. 6. 12.
5. Longest Palindromic Substring [Strings, dynamic programming] Problems: Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000. Example 1: Input: "babad" Output: "bab" Note: "aba" is also a valid answer. Example 2: Input: "cbbd" Output: "bb" -Summary- Approach: Expand around the center 1. Two cases exist. - Palindrome with odd lengths of string (example: 'aba', 'abcba') --> where 1 character in th.. 2020. 6. 11.
LeetCode. Search Insert Position [Binary Search] Problem: Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order. You may assume no duplicates in the array. Example 1: Input: [1,3,5,6], 5 Output: 2 Example 2: Input: [1,3,5,6], 2 Output: 1 Example 3: Input: [1,3,5,6], 7 Output: 4 Example 4: Input: [1,3,5,6], 0 Output: 0 -Summary- 1. if the target .. 2020. 6. 11.
LeetCode. Maximum Subarray [Dynamic Programming] Problem: Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum. Example: Input: [-2,1,-3,4,-1,2,1,-5,4], Output: 6 Explanation: [4,-1,2,1] has the largest sum = 6. Follow up: If you have figured out the O(n) solution, try coding another solution using the divide and conquer approach, which is more subtle. -Summary-.. 2020. 6. 11.
LeetCode. Is Subsequence Problem: Given a string s and a string t, check if s is subsequence of t. A subsequence of a string is a new string which is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (ie, "ace" is a subsequence of "abcde" while "aec" is not). Follow up: If there are lots of incoming S, say S1, S2, ... ,.. 2020. 6. 10.

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