leetcode-264-丑数

题目描述：

 

 方法一：堆 O(nlogn)

class Solution:
    def nthUglyNumber(self, n: int) -> int:
        import heapq
        heap = [1]
        res = 0
        heapq.heapify(heap)
        for _ in range(n):
            res = heapq.heappop(heap)
            while heap and res == heap[0]:
                res = heapq.heappop(heap)
            a,b,c = res*2,res*3,res*5
            for t in [a,b,c]:
                heapq.heappush(heap,t)
        return res

方法二：动态规划 O(N)

class Solution:
    def nthUglyNumber(self, n: int) -> int:
        dp = [0] * n
        dp[0] = 1
        l2,l3,l5 = 0,0,0
        for i in range(1,n):
            dp[i] = min(dp[l2]*2,dp[l3]*3,dp[l5]*5)
            if dp[i]>=dp[l2]*2:
                l2 += 1
            if dp[i]>=dp[l3]*3:
                l3 += 1
            if dp[i]>=dp[l5]*5:
                l5 += 1
        return dp[-1]