pr

kaakxixi/contains_duplicate_2.py

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+"""
+Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the absolute difference between i and j is at most k.
+"""
+"""仍然用dict保存数组元素出现的位置，两种情况下更新"""
+
+class Solution(object):
+    def containsDuplicate2(self,nums,k):
+        dic = dict()
+        for index,value in enumerate(nums):
+            if value in dic and  index - dic[value] <= k:
+                return True
+            dic[value] = index
+        return False

kaakxixi/intersection_of_two_arrays.py

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+"""
+Given two arrays, write a function to compute their intersection.
+Example:
+Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2].
+"""
+
+"""可以使用hash table保存下数组1的出现的元素，然后判断数组2中的各元素是否在数组1中出现过，但直接使用set更简单"""
+class Solution(object):
+    def intersectionOfTwoArrays(self,nums1,nums2):
+        """
+        :type nums1: List[int]
+        :type nums2: List[int]
+        :rtype: List[int]
+        """
+        result = []
+        for value in set(nums1):
+            if value in set(nums2):
+                result.append(value)
+        return result
+
+        '''利用列表表达式'''
+        return [i for i in set(nums1) if i in set(nums2)]

kaakxixi/intersection_of_two_arrays_2.py

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+"""
+Given two arrays, write a function to compute their intersection.
+Example:
+Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2, 2].
+Note:
+Each element in the result should appear as many times as it shows in both arrays.
+The result can be in any order.
+Follow up:
+What if the given array is already sorted? How would you optimize your algorithm?
+What if nums1's size is small compared to nums2's size? Which algorithm is better?
+What if elements of nums2 are stored on disk, and the memory is limited such that you cannot load all elements into the memory at once?
+"""
+"""使用两个字典记录下两个数组中元素出现的次数"""

kaakxixi/readme.md

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+LeetCode 1 两数之和 
+2018-12-05
+代码提交地址 https://leetcode-cn.com/problems/two-sum/submissions/
+
+算法分析：
+
+方法1. 整体时间复杂度为O(n^2). 由于python中的list对象实际上是链表，其查询效率为 O(n), 即这里的if 语句if num in nums复杂度为O(n),
+再结合列表循环次数n, 整体时间复杂度为O(n^2).
+
+方法2. 整体时间复杂度为常数级别O(1). 使用散列hash表(python中的dict和set), 将差值target - nums[i]作为dict的键, 索引 i 作为dict的值, 判断列表中的值是否在dict中, 这里对hash表中的元素的访问是常数时间级别.
+

kaakxixi/sum_two_nums.py

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+"""
+给定一个整数数组 nums 和一个目标值 target，请你在该数组中找出和为目标值的那 两个 整数，并返回他们的数组下标。
+
+你可以假设每种输入只会对应一个答案。但是，你不能重复利用这个数组中同样的元素。
+
+示例:
+
+给定 nums = [2, 7, 11, 15], target = 9
+
+因为 nums[0] + nums[1] = 2 + 7 = 9
+所以返回 [0, 1]
+"""
+"""方法1是使用list查询差值"""
+class Solution(object):
+    def twoSum(self, nums, target):
+        """
+        :type nums: List[int]
+        :type target: int
+        :rtype: List[int]
+        """
+        for i in range(len(nums)):
+            num = target - nums[i]
+            if num in nums and nums.index(num) != i:
+                return [i,nums.index(num)]
+
+
+"""方法2是使用dict查询差值"""
+    def twoSum2(self, nums, target):
+        """
+        :type nums: List[int]
+        :type target: int
+        :rtype: List[int]
+        """           
+        #创建一个空字典
+        dic = {}
+        for i in range(len(nums)):
+            num = target - nums[i]
+            #字典d中存在nums[i]时
+            if nums[i] in dic:
+                return dic[nums[i]],i
+            #否则往字典增加键/值对
+            else:
+                dic[num] = i
+        #边往字典增加键/值对，边与nums[i]进行对比

kaakxixi/valid_anagram.py

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+"""
+Given two strings s and t, write a function to determine if t is an anagram of s.
+For example,
+s = "anagram", t = "nagaram", return true.
+s = "rat", t = "car", return false.
+Note:
+You may assume the string contains only lowercase alphabets.
+"""
+"""用两个字典保存字符出现的情况，判断两个字典是否相同即可"""
+class Solution(object):
+    def validAnagram(self,s,t):
+        dic1 = {}
+        dic2 = {}
+        for i in s:
+            dic1[i] = dic1.get(i,0) + 1
+        for j in t:
+            dic2[j] = dic2.get(j,0) + 1
+        return dic1 == dic2

kaakxixi/word_pattern.py

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+"""
+Total Accepted: 76577
+Total Submissions: 233596
+Difficulty: Easy
+Contributor: LeetCode
+Given a pattern and a string str, find if str follows the same pattern.
+Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in str.
+Examples:
+pattern = "abba", str = "dog cat cat dog" should return true.
+pattern = "abba", str = "dog cat cat fish" should return false.
+pattern = "aaaa", str = "dog cat cat dog" should return false.
+pattern = "abba", str = "dog dog dog dog" should return false.
+Notes:
+You may assume pattern contains only lowercase letters, and str contains lowercase letters separated by a single space.
+"""
+class Solution(object):
+    def wordPattern(self,pattern,str):
+        """
+        :type pattern: str
+        :type str: str
+        :rtype: bool
+        """
+        return len(pattern) == len(str.split(' ')) and len(set(pattern)) == len(
+            set(str.split(' '))) == len(set(zip(pattern,str.split(' '))))