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[LeetCode] 921. Minimum Add to Make Parentheses Valid

A parentheses string is valid if and only if: It is the empty string, It can be written as AB (A concatenated with B), where A and B are valid strings, or It can be written as (A), where A is a valid

2020-12-18

#leetcode #java #greedy #stack

[LeetCode] 1669. Merge In Between Linked Lists

You are given two linked lists: list1 and list2 of sizes n and m respectively. Remove list1’s nodes from the ath node to the bth node, and put list2 in their place. The blue edges and nodes in the fol

2020-12-15

#leetcode #java #linked list

[LeetCode] 1609. Even Odd Tree

A binary tree is named Even-Odd if it meets the following conditions:The root of the binary tree is at level index 0, its children are at level index 1, their children are at level index 2, etc.For ev

2020-12-10

#leetcode #java #tree #bfs

[LeetCode] 1325. Delete Leaves With a Given Value

Given a binary tree root and an integer target, delete all the leaf nodes with value target. Note that once you delete a leaf node with value target, if its parent node becomes a leaf node and has the

2020-12-02

#leetcode #java #tree #postorder #recursion

[LeetCode] 814. Binary Tree Pruning

Given the root of a binary tree, return the same tree where every subtree (of the given tree) not containing a 1 has been removed. A subtree of a node node is node plus every node that is a descendant

2020-12-02

#leetcode #java #tree #postorder

[LeetCode] 1010. Pairs of Songs With Total Durations Divisible by 60

You are given a list of songs where the ith song has a duration of time[i] seconds. Return the number of pairs of songs for which their total duration in seconds is divisible by 60. Formally, we want

2020-11-28

#leetcode #array #hashmap #java #two sum #counting sort #MOD

[LeetCode] 395. Longest Substring with At Least K Repeating Characters

Given a string s and an integer k, return the length of the longest substring of s such that the frequency of each character in this substring is greater than or equal to k. if no such substring exist

2020-11-27

#leetcode #hashmap #java #sliding window #string #divide and conquer

[LeetCode] 1404. Number of Steps to Reduce a Number in Binary Representation to One

Given the binary representation of an integer as a string s, return the number of steps to reduce it to 1 under the following rules:If the current number is even, you have to divide it by 2.If the cur

2020-11-23

#leetcode #java #string #bit manipulation

[LeetCode] 1582. Special Positions in a Binary Matrix

Given an m x n binary matrix mat, return the number of special positions in mat. A position (i, j) is called special if mat[i][j] == 1 and all other elements in row i and column j are 0 (row

2020-11-14

#leetcode #array #hashmap #java

[LeetCode] 1283. Find the Smallest Divisor Given a Threshold

Given an array of integers nums and an integer threshold, we will choose a positive integer divisor, divide all the array by it, and sum the division’s result. Find the smallest divisor such that the

2020-11-07

#leetcode #array #java #binary search