Weekly Contest 309

Weekly Contest 309

Problem A

Check Distances Between Same Letters

思路

水题，遍历数组然后check一下就行

代码

    class Solution:
    def checkDistances(self, s: str, distance: List[int]) -> bool:
        
        for i in range(len(s)):
            print(i)
            d =  distance[ord(s[i])-ord('a')]
            # print(s[i],s[i+d+1])
            if i+d+1>=len(s) or s[i]!=s[i+d+1]:
                return False
            distance[ord(s[i])-ord('a')] = -1
        return True

Problem B

Number of Ways to Reach a Position After Exactly k Steps

思路

组合数推理，做的时候想复杂了，本质上是求k步中向左走x步（或者是向右走y步,x+y=k）的组合数，组合数取模要用到费马小定理(python 有comb)

代码

    class Solution:
      def numberOfWays(self, a, b, k):
        if (a - b - k) % 2: return 0
        return comb(k, (b - a + k) // 2) % (10 ** 9 + 7)

Problem C

Longest Nice Subarray

思路

求一个连续的子序列，用滑动窗口去解决，任意两个数“与”为0，就是任意两个数二进制中不能出现同一位为1的情况。

代码

class Solution:
    def longestNiceSubarray(self, nums: List[int]) -> int:
        self.D = 0
        i ,j=0,1
        self.check(nums[i])
        l = len(nums)
        ans = 1
        while(j<l):
            print(i)
            if self.check(nums[j]) is False:
                # print("UPDATA")
                ans = max(ans,j-i)
                while(i<j and self.D & nums[j]!=0):
                    self.D-=nums[i]
                    # print(self.D)
                    i+=1
                self.D+=nums[j]
                
            j+=1
            # print(i,j,self.D)
        ans = max(ans,j-i)
        return ans
    def check(self,x):
        if x & self.D == 0:
            self.D = self.D+x
            return True
        else:
            
            return False

Problem D

Meeting Rooms III

思路

优先队列(python里面没有，只有最小堆-heap)，需要特殊处理的是某些meeting到时有好几个room是空的，所以要找这些room里面最小的

代码

class Solution:
    def mostBooked(self, n: int, meetings: List[List[int]]) -> int:
        L = []
        t = []
        meetings.sort()
        # print(meetings)
        for i in range(n):
            L.append([0,i])
            t.append(0)
        heapq.heapify(L)
        for item in meetings:
            temp = []
            while(len(L)!=0):
                
                _ = heapq.heappop(L)
                # print(_)
                if _[0]<=item[0]:
                    temp.append(_)
                else:
                    heapq.heappush(L,_)
                    break
            if len(temp)==0:
                _ = heapq.heappop(L)
                # print(item,_[1])
                t[_[1]]+=1
                _[0] = max(_[0],item[0])+item[1]-item[0]
                heapq.heappush(L,_)
            else:
                l,_ = 0,temp[0][1]
                for i in range(1,len(temp)):
                    if temp[i][1]<_:
                        _ = temp[i][1]
                        l = i
                # print(item,_)
                t[_]+=1
                temp[l][0] = max(temp[l][0],item[0])+item[1]-item[0]
                for item in temp:
                    heapq.heappush(L,item)
                
        M,ans= t[0],0
        # print(t)
        for i in range(1,n):
            if t[i]>M:
                M= t[i]
                ans = i
        return ans

总结

真菜啊