# Daily Archives: February 23, 2015

## [leetcode] Generate Parentheses

Generate Parentheses Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses. For example, given n = 3, a solution set is: “((()))”, “(()())”, “(())()”, “()(())”, “()()()” tag: backtracking 7/10/2015 udpate DFS approach, add some restrictions to guarantee the validation of parentheses class Solution { […]

## [leetcode] Valid Parentheses

Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[‘ and ‘]’, determine if the input string is valid. The brackets must close in the correct order, “()” and “()[]{}” are all valid but “(]” and “([)]” are not. tag: stack, string 5/10/2015 update a neater approach, with […]

## [leetcode] Remove Nth Node From End of List

Given a linked list, remove the nth node from the end of list and return its head. For example, Given linked list: 1->2->3->4->5, and n = 2. After removing the second node from the end, the linked list becomes 1->2->3->5. Note: Given n will always be valid. Try to do […]

## [leetcode] 4sum

Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target. Note: Elements in a quadruplet (a,b,c,d) must be in […]