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原创 Leetcode 108. Convert Sorted Array to Binary Search Tree

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the ...

2019-01-18 06:39:35 246

原创 Leetcode 105 & 106. Construct Binary Tree from Preorder and Inorder & Inorder and Postorder

hashUse a dictionary to store the number in inorder and its index. Find position of the root in inorder in O(1).slow version# Definition for a binary tree node.# class TreeNode:# def __init__...

2019-01-18 05:36:16 203

原创 Leetcode 103. Binary Tree Zigzag Level Order Traversal

# Definition for a binary tree node.# class TreeNode:# def __init__(self, x):# self.val = x# self.left = None# self.right = Noneclass Solution: def zigzagLevelOr...

2019-01-18 04:51:46 175

原创 Leetcode 102 & 107. Binary Tree Level Order Traversal I & II

Binary Tree Level Order TraversalGiven a binary tree, return the bottom-up level order traversal of its nodes’ values. (ie, from left to right, level by level from leaf to root).For example:Given...

2019-01-18 03:41:03 177

原创 Leetcode 104 & 111. Minimum & Maximum Depth of Binary Tree

Maximum Depth of Binary Tree# Definition for a binary tree node.# class TreeNode:# def __init__(self, x):# self.val = x# self.left = None# self.right = Noneclass So...

2019-01-07 07:27:14 168

原创 Leetcode 100 & 101. Same Tree & Symmetric Tree

# Definition for a binary tree node.# class TreeNode:# def __init__(self, x):# self.val = x# self.left = None# self.right = Noneclass Solution: def isSameTree(se...

2019-01-07 03:33:12 173

原创 Leetcode 99. Recover Binary Search Tree

# Definition for a binary tree node.# class TreeNode:# def __init__(self, x):# self.val = x# self.left = None# self.right = Noneclass Solution: def recoverTree(s...

2019-01-07 03:31:36 202

原创 Leetcode 98. Validate Binary Search Tree

Same method to inorder traversal# Definition for a binary tree node.# class TreeNode(object):# def __init__(self, x):# self.val = x# self.left = None# self.right = No...

2019-01-02 05:39:04 145

原创 Leetcode 95 & 96. Unique Binary Search Trees I & II

Unique Binary Search Trees IGiven n, how many structurally unique BST’s (binary search trees) that store values 1 … n?Example:Input: 3Output: 5class Solution(object): def numTrees(self, n)...

2019-01-02 05:04:54 167

原创 Leetcode 94 & 102 & 144 & 145. Binary Tree Traversal (dfs & bfs)

stack# Definition for a binary tree node.# class TreeNode:# def __init__(self, x):# self.val = x# self.left = None# self.right = Noneclass Solution: def inorder...

2018-12-31 20:00:57 207

原创 Leetcode 89. Gray Code

2 solutionsclass Solution: def grayCode(self, n): """ :type n: int :rtype: List[int] """ return map(lambda x:int(x,2),self.gray(n)) def gray(self,n):...

2018-12-31 19:36:00 168

原创 Leetcode 88. Merge Sorted Array

class Solution: def merge(self, nums1, m, nums2, n): """ :type nums1: List[int] :type m: int :type nums2: List[int] :type n: int :rtype: void Do no...

2018-12-31 07:49:46 162

原创 Leetcode 86. Partition List

# Definition for singly-linked list.# class ListNode:# def __init__(self, x):# self.val = x# self.next = Noneclass Solution: def partition(self, head, x): """ ...

2018-12-31 07:08:29 168

原创 Leetcode 85. Maximal Rectangle

same method to leetcode 84reference:https://blog.youkuaiyun.com/doc_sgl/article/details/11832965https://www.cnblogs.com/lupx/archive/2015/10/20/leetcode-85.htmlclass Solution(object): def maximalRec...

2018-12-31 06:52:27 217

原创 Leetcode 84. Largest Rectangle in Histogram

stackexplaination(small mistakes in the graphs): http://www.cnblogs.com/lichen782/p/leetcode_Largest_Rectangle_in_Histogram.htmlclass Solution(object): def largestRectangleArea(self, height): ...

2018-12-31 04:18:52 169

原创 Leetcode 82&83. Remove Duplicates from Sorted List I & II

recursion can be used in IIdifference between pre=cur(the same node) and pre.val=cur.val (two nodes have the same number)Remove Duplicates from Sorted List I2 solutionsslow version# Definition fo...

2018-12-31 00:24:20 182

原创 Leetcode81. Search in Rotated Sorted Array II

class Solution: def search(self, nums, target): """ :type nums: List[int] :type target: int :rtype: bool """ left=0 right=len(nums)-1

2018-12-30 23:30:25 146

原创 Leetcode 80. Remove Duplicates from Sorted Array II

2 methodsclass Solution(object): def removeDuplicates(self, nums): """ :type nums: List[int] :rtype: int """ if not nums: return 0 newT...

2018-12-30 09:35:30 155

原创 Leetcode 79. Word Search

dfs66.9%class Solution: def exist(self, board, word): """ :type board: List[List[str]] :type word: str :rtype: bool """ def dfs(index,row...

2018-12-30 09:18:19 158

原创 Leetcode 78 & 90. Subsets I&II

class Solution: def subsets(self, nums): """ :type nums: List[int] :rtype: List[List[int]] """ res=[] self.dfs(nums,0,[],res) return r

2018-12-30 00:44:53 187

原创 Leetcode 77. Combinations

recursion &dfsrecursion(slow)class Solution: def combine(self, n, k): """ :type n: int :type k: int :rtype: List[List[int]] """ res = [] ...

2018-12-29 06:52:33 231

原创 Leetcode 76. Minimum Window Substring

sliding window: find a window that contains all the characters in t, then reduce the window by moving start pointer but still contains all the characters.class Solution: def minWindow(self, s, t)...

2018-12-29 06:10:35 173

原创 Leetcode 75. Sort Colors

Two pointersleft points to the position that 0 endsright points to the position that 2 beginsclass Solution: def sortColors(self, nums): """ :type nums: List[int] :rtype...

2018-12-29 04:48:23 143

原创 Leetcode 74. Search a 2D Matrix

Binary Searchposition01234567891011number1458911121517182022row000011112222col012301230123row=position//4col=position%4

2018-12-29 03:11:11 154

原创 Leetcode 73. Set Matrix Zeroes

class Solution: def setZeroes(self, matrix): """ :type matrix: List[List[int]] :rtype: void Do not return anything, modify matrix in-place instead. """

2018-12-29 00:38:17 136

原创 Leetcode 70. Climbing Stairs

recursion & dp(Fibonacci Number)Recursion!TLEclass Solution: def climbStairs(self, n): """ :type n: int :rtype: int """ if n == 1: retur...

2018-12-28 23:43:58 138

原创 Leetcode 69. Sqrt(x)

Binary Search and Newton MethodBinary Searchclass Solution: def mySqrt(self, x): """ :type x: int :rtype: int """ l, r = 0, x while l &

2018-12-27 06:29:17 130

原创 Leetcode 68. Text Justification

class Solution: def fullJustify(self, words, maxWidth): """ :type words: List[str] :type maxWidth: int :rtype: List[str] """ res, cur, num_of_l

2018-12-27 06:25:04 267

原创 Leetcode 67. Add Binary

class Solution: def addBinary(self, a, b): """ :type a: str :type b: str :rtype: str """ m=len(a)-1 n=len(b)-1 res=''

2018-12-27 06:07:00 133

原创 Leetcode 66. Plus One

99.83%class Solution: def plusOne(self, digits): """ :type digits: List[int] :rtype: List[int] """ res=[] tmp=0 for i in digits[::-1

2018-12-27 01:02:19 132

原创 Leetcode 65. Valid Number

s=s.strip() delete the space front and end.‘e’ can only appear after digits and ‘.’ cannot appear after ‘e’. In other words, the character before ‘e’ and after ‘e’ must be both digits. (e3 and 3e ar...

2018-12-27 00:38:19 191

原创 Leetcode 64. Minimum Path Sum

class Solution: def minPathSum(self, grid): """ :type grid: List[List[int]] :rtype: int """ m=len(grid) n=len(grid[0]) for i in range(m): ...

2018-12-26 01:36:48 139

原创 Leetcode 62 & 63. Unique Paths I &II

key point: Unique Paths II fast versionUnique Paths Iclass Solution: def uniquePaths(self, m, n): """ :type m: int :type n: int :rtype: int """ dp...

2018-12-26 01:22:34 142

原创 Leetcode 61. Rotate List

Calculate the length of the list and use k%length.# Definition for singly-linked list.# class ListNode:# def __init__(self, x):# self.val = x# self.next = Noneclass Solution...

2018-12-26 00:29:28 141

原创 Leetcode 57. Insert Interval

# Definition for an interval.# class Interval:# def __init__(self, s=0, e=0):# self.start = s# self.end = eclass Solution: def insert(self, intervals, newInterval): ...

2018-12-13 04:59:57 141

原创 Leetcode 56. Merge Intervals

# Definition for an interval.# class Interval:# def __init__(self, s=0, e=0):# self.start = s# self.end = eclass Solution: def merge(self, intervals): """ ...

2018-12-13 03:22:22 130

原创 Leetcode 45&55. Jump Game I &II

There are many solutions for these two problems. For Jump Game I, greedy is the best method, but we can also use DP to solve it.Jump Game ISolution 1 DPThere are two kind of DP solution, bottom-up...

2018-12-13 01:02:27 246

原创 Leetcode 60. Permutation Sequence

n=4,k=9There are 4 groups of n=4 (1-6,7-12,13-18,19-24), 9 belongs to the second one. So the first number is the second one of [1,2,3,4], which is 2.There are 3 groups of n=3 (1-2,3-4,5-6), the rema...

2018-12-12 08:36:11 160

原创 Leetcode 58. Length of Last Word

special case “a b ”class Solution(object): def lengthOfLastWord(self, s): """ :type s: str :rtype: int """ result=0 index=len(s)-1 whi...

2018-12-12 07:58:26 136

原创 Leetcode 54 & 59. Spiral Matrix I & II

Spiral Matrix Iclass Solution: def spiralOrder(self, matrix): """ :type matrix: List[List[int]] :rtype: List[int] """ if len(matrix) == 0: retu...

2018-12-12 07:08:58 181

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