算法之：练习题

一、重排列

 方法一：

class Solution:
    def isAnagram(self,s,t):
        """
        :param s: str
        :param t: str
        :return: bool
        """
        dict1 = {} #{'a':1,'b':2}
        dict2 = {}
        for ch in s:
            dict1[ch] = dict1.get(ch,0) + 1
        for ch in t:
            dict2[ch] = dict2.get(ch,0) + 1
        return dict1 == dict2

方法二：

class Solution:
    def isAnagram(self, s, t):
        """
        :param s: str
        :param t: str
        :return: bool
        """
        return sorted(list(s)) == sorted(list(t))

二、二维二分查找

 

方法一：

class Solution:
    def searchMatrix(self, matrix, target):
        """
        :param matrix: List[List[int]]
        :param target: int
        :return: bool
        """
        #[[],[],[]]
        m = len(matrix) # 行数
        if m == 0:
            return False
        n = len(matrix[0])  #列数
        if n == 0:
            return False
        low = 0
        high = m * n - 1

        while low <= high:
            mid =(low + high) // 2
            x,y = divmod(mid,n)

            if matrix[x][y] > target:
                high = mid - 1
            elif matrix[x][y] < target:
                low = mid + 1
            else:
                return True
        else:
            return  False

方法二：

class Solution:
    def searchMatrix(self, matrix, target):
        if not matrix or target is None:
            return False

        rows,cols = len(matrix), len(matrix[0])
        low, high = 0,rows * cols - 1

        while low <= high:
            mid = (low + high) / 2
            num = matrix[mid / cols][mid % cols]

            if num == target:
                return  True
            elif num < target:
                low = mid + 1
            else:
                high = mid + 1
        return False

三、 Two Sum

1、题目描述

2、方法一

class Solution:
    def binary_search(self,li,left,right,val):
        while left <= right:   #候选区有值
            mid = (left + right) // 2
            if li[mid][0] == val:
                return mid
            elif li[mid][0] > val:  #待查找的值在mid左侧
                right = mid - 1
            else: #li[mid]< val 待查找的值在mid右侧
                left = mid + 1
        else:
            return None
def twoSum(self,nums,trarget):
    """
    :param self:
    :param nums: List[int]
    :param trarget: int
    :return:
    """

    new_nums = [[num,i] for i,num in enumerate(nums)]
    new_nums.sort(key = lambda  x:x[0])
    for i in range(len(new_nums)):
        a = new_nums[i][0]
        b = trarget - a
        if b >= a:
        #print(b,i+1,len(nums)-1)
            j = self.binary_search(new_nums,i+1,len(nums)-1,b)
        else:
            j = self.binary_search(new_nums, 0, i - 1, b)
        if j:
            return sorted([new_nums[i][1],new_nums[j][1]])

3、方法二

def twoSum(self,nums,trarget):
    """
    :param self:
    :param nums: List[int]
    :param trarget: int
    :return: List[int]
    """
    #[1,4,6,7,9,3], 9
    #{1:0,4:1,6:2,7:3,9:4}
    d = {}
    for i in range(len(nums)):
        a = nums[i]
        b = trarget - a
        if b in d:
            return [d[b],i]
        else:
            d[a] = i　

https://leetcode.com/problems/two-sum/description/

四、区域查询

 方法一：

def find_a(nums,target):
    low = 0
    high = len(nums) - 1
    while low <= high:
        mid = (low + high) // 2
        if target <= nums[mid]:
            high = mid - 1
        else:
            low = mid + 1

    #[1,2,3,2,4,8,10]

    if low < len(nums):
        return low
    else:
        return  -1

def find_b(nums,target):
    low = 0
    high = len(nums) - 1
    while low <= high:
        mid = (low + high) // 2
        if target < nums[mid]:
            high = mid - 1
        else:
            low = mid + 1
    if low < len(nums):
        return low
    else:
        return -1