README_EN.md

264. Ugly Number II

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Description

An ugly number is a positive integer whose prime factors are limited to 2, 3, and 5.

Given an integer n, return the nth ugly number.

 

Example 1:

Input: n = 10
Output: 12
Explanation: [1, 2, 3, 4, 5, 6, 8, 9, 10, 12] is the sequence of the first 10 ugly numbers.

Example 2:

Input: n = 1
Output: 1
Explanation: 1 has no prime factors, therefore all of its prime factors are limited to 2, 3, and 5.

 

Constraints:

• 1 <= n <= 1690

Solutions

Python3

class Solution:
    def nthUglyNumber(self, n: int) -> int:
        dp = [1] * n
        p2 = p3 = p5 = 0
        for i in range(1, n):
            next2, next3, next5 = dp[p2] * 2, dp[p3] * 3, dp[p5] * 5
            dp[i] = min(next2, next3, next5)
            if dp[i] == next2:
                p2 += 1
            if dp[i] == next3:
                p3 += 1
            if dp[i] == next5:
                p5 += 1
        return dp[n - 1]

Java

class Solution {
    public int nthUglyNumber(int n) {
        int[] dp = new int[n];
        dp[0] = 1;
        int p2 = 0, p3 = 0, p5 = 0;
        for (int i = 1; i < n; ++i) {
            int next2 = dp[p2] * 2, next3 = dp[p3] * 3, next5 = dp[p5] * 5;
            dp[i] = Math.min(next2, Math.min(next3, next5));
            if (dp[i] == next2) ++p2;
            if (dp[i] == next3) ++p3;
            if (dp[i] == next5) ++p5;
        }
        return dp[n - 1];
    }
}

C++

class Solution {
public:
    int nthUglyNumber(int n) {
        vector<int> dp(n);
        dp[0] = 1;
        int p2 = 0, p3 = 0, p5 = 0;
        for (int i = 1; i < n; ++i) {
            int next2 = dp[p2] * 2, next3 = dp[p3] * 3, next5 = dp[p5] * 5;
            dp[i] = min(next2, min(next3, next5));
            if (dp[i] == next2) ++p2;
            if (dp[i] == next3) ++p3;
            if (dp[i] == next5) ++p5;
        }
        return dp[n - 1];
    }
};

JavaScript

/**
 * @param {number} n
 * @return {number}
 */
var nthUglyNumber = function (n) {
  let dp = [1];
  let p2 = 0,
    p3 = 0,
    p5 = 0;
  for (let i = 1; i < n; ++i) {
    const next2 = dp[p2] * 2,
      next3 = dp[p3] * 3,
      next5 = dp[p5] * 5;
    dp[i] = Math.min(next2, Math.min(next3, next5));
    if (dp[i] == next2) ++p2;
    if (dp[i] == next3) ++p3;
    if (dp[i] == next5) ++p5;
    dp.push(dp[i]);
  }
  return dp[n - 1];
};

Go

func nthUglyNumber(n int) int {
    dp := make([]int, n)
    dp[0] = 1
    p2, p3, p5 := 0, 0, 0
    for i := 1; i < n; i++ {
        next2, next3, next5 := dp[p2]*2, dp[p3]*3, dp[p5]*5
        dp[i] = min(next2, min(next3, next5))
        if dp[i] == next2 {
            p2++
        }
        if dp[i] == next3 {
            p3++
        }
        if dp[i] == next5 {
            p5++
        }
    }
    return dp[n-1]
}

func min(a, b int) int {
    if a < b {
        return a
    }
    return b
}

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