技術標籤：LeetCode刷題

題號169

方法1：排序法
對陣列排序，重複的元素會排在一起，題目定義的多數元素為陣列中出現次數 大於 ⌊ n/2 ⌋ 的元素，對排序後的陣列求中間元素值，這個中間元素就是多數元素

class Solution:
    def majorityElement(self, nums: List[int]) -> int:
        nums.sort()
        left = 0
        right =len(nums)-1
        mid = (left+right)//2
        n = nums[mid]
        return
 
 n

方法2：雜湊表
統計陣列中每個元素出現的次數，遍歷key，找key的值大於 ⌊ n/2 ⌋ 的元素

class Solution:
    def majorityElement(self, nums: List[int]) -> int:
        dict={}
        for num in nums:
            if num not in dict:
                dict[num]=0
            
            dict[num]=dict.get(num)+1
        mid = len(nums)
 
//2
        for key in dict.keys():
            if dict[key]>mid:
                return key
        return -1
        

題號200

方法1：DFS

class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        if len(grid)==0:
            return 0
        row = len(grid)
        col = len(grid[
 
0])
        count =0
        for r in range (row):
            for c in range (col):
                if grid[r][c] == '1':
                    count+=1
                    self.DFS(grid,r,c)
        return count
    
    def DFS(self,grid,r,c):
        if r<0 or c<0 or r>=len(grid) or c>=len(grid[0]) or grid[r][c]== '0':
            return 0
        grid[r][c]='0'
        self.DFS(grid,r+1,c)
        self.DFS(grid,r-1,c)
        self.DFS(grid,r,c+1)
        self.DFS(grid,r,c-1)

Python獲取二維陣列的行列數