Special Leetcode of dynamic programming (DP) -264. Ugly Number II (Ugly Number II)

Special Leetcode of dynamic programming (DP) -264. Ugly Number II (Ugly Number II)

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Write a program to find the first  n one ugly number.

Ugly is the number contains only prime factors  2, 3, 5 of positive integers.

Example:

Input: n = 10 
Output: 12 
Explanation: The 1, 2, 3, 4, 5, 6, 8, 9, 10, 12first 10 ugly number.

Description:  

1. 1 Is the number of ugly.
2. n Not more than 1690.

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dp meaning:

dp [i] denotes the i-1 th number of ugly.

 

class Solution {
    public int nthUglyNumber(int n) {
        int[] dp = new int[n + 1];
        dp[0] = 1;
        int i2 = 0;
        int i3 = 0;
        int i5 = 0;
        for (int i = 1; i < n + 1; i++) {
            dp[i] = Math.min(Math.min(dp[i2] * 2, 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];
    }
}