leetcode/cpp/0264.cpp at master · xfmeng17/leetcode · GitHub

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class Solution {
public:
  int nthUglyNumber(int n) {
    // return func1(n);
    return func2(n);
  }

  // ** hash set
  // ** TLE
  int func1(int n) {
    unordered_set<int> table;
    table.insert(1);
    int len = 1;
    int curr = 1;
    int last = 1;

    while (table.size() < n) {
      curr++;
      if (curr % 2 == 0 && table.count(curr / 2) > 0) {
        table.insert(curr);
        last = curr;
      } else if (curr % 3 == 0 && table.count(curr / 3) > 0) {
        table.insert(curr);
        last = curr;
      } else if (curr % 5 == 0 && table.count(curr / 5) > 0) {
        table.insert(curr);
        last = curr;
      }
    }

    return last;
  }

  // ** Reference
  int func2(int n) {
    if (n <= 0)
      return 0;
    if (n == 1)
      return 1;
    int i2 = 0, i3 = 0, i5 = 0;
    vector<int> dp(n, 0);
    dp[0] = 1;
    for (int i = 1; i < n; i++) {
      dp[i] = min(dp[i2] * 2, min(dp[i3] * 3, dp[i5] * 5));
      if (dp[i] == dp[i2] * 2)
        i2++;
      if (dp[i] == dp[i3] * 3)
        i3++;
      if (dp[i] == dp[i5] * 5)
        i5++;
    }

    return dp[n - 1];
  }
};