题目大意：让你找到第n个丑数。
Problem:
Write a program to find the n-th ugly number.
Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers.
Note that 1 is typically treated as an ugly number, and n does not exceed 1690.
Solution:
C++ / O(n)
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// Author: huahua // Running time: 6 ms class Solution { public: int nthUglyNumber(int n) { static vector<int> nums{1}; static int i2 = 0; static int i3 = 0; static int i5 = 0; while (nums.size() < n) { const int next2 = nums[i2] * 2; const int next3 = nums[i3] * 3; const int next5 = nums[i5] * 5; const int next = min(next2, min(next3, next5)); if (next == next2) ++i2; if (next == next3) ++i3; if (next == next5) ++i5; nums.push_back(next); } return nums[n - 1]; } }; |
C++ /query * O(NlogN)
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// Author: Huahua // Running time: 89 ms class Solution { public: int nthUglyNumber(int n) { vector<int> nums; for (long a = 1; a <= INT_MAX; a *= 2) for (long b = a; b <= INT_MAX; b *= 3) for (long c = b; c <= INT_MAX; c *= 5) nums.push_back(c); std::sort(nums.begin(), nums.end()); return nums[n - 1]; } }; |
C++ / static variables O(NlogN) + query*O(1)
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// Author: Huahua // Running time: 7 ms class Solution { public: int nthUglyNumber(int n) { static vector<int> nums; if (nums.empty()) { for (long a = 1; a <= INT_MAX; a *= 2) for (long b = a; b <= INT_MAX; b *= 3) for (long c = b; c <= INT_MAX; c *= 5) nums.push_back(c); std::sort(nums.begin(), nums.end()); } return nums[n - 1]; } }; |
C++ / table O(1)
leetcode_264_table.cc
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