Problem_0264_nthUglyNumber.cc

#include <algorithm>
#include <vector>

using namespace std;

class Solution
{
 public:
  // 时间复杂度O(n)，n代表第n个丑数
  int nthUglyNumber(int n)
  {
    // dp 0 1 2 ... n
    //      1 2 ... ?
    vector<int> dp(n + 1);
    dp[1] = 1;
    for (int i = 2, i2 = 1, i3 = 1, i5 = 1, a, b, c, cur; i <= n; i++)
    {
      a = dp[i2] * 2;
      b = dp[i3] * 3;
      c = dp[i5] * 5;
      cur = std::min({a, b, c});
      if (cur == a)
      {
        i2++;
      }
      if (cur == b)
      {
        i3++;
      }
      if (cur == c)
      {
        i5++;
      }
      dp[i] = cur;
    }
    return dp[n];
  }
};