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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. |
题意：找第N个丑数。N<1690.
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public class Solution {
public int nthUglyNumber(int n) {
int[] result=new int[n];
result[0]=1;
int begin=1;
int m2=0,m3=0,m5=0;
while(begin<n){
result[begin]=min(result[m2]*2,result[m3]*3,result[m5]*5);
// System.out.println(result[begin]);
while(result[m2]*2<=result[begin]){
m2++;
}
while(result[m3]*3<=result[begin]){
m3++;
}
while(result[m5]*5<=result[begin]){
m5++;
}
begin++;
}
return result[--begin];
}
public static int min(int m2,int m3,int m5){
int temp=m2<m3?m2:m3;
return m5<temp?m5:temp;
}
} |
PS:要是利用前面的一个一个丑数挨个算到第N个，效率会很低。此时我们利用后面的丑数都是由前面的丑数*2，*3，*5得到，保存前面得到的丑数，就没有必要计算所有的了。效率提升。思路见剑指offer P183。
本文转自 努力的C 51CTO博客，原文链接:http://blog.51cto.com/fulin0532/1905432