lintcode: Ugly Number II

Ugly number is a number that only have factors 2, 3 and 5.

Design an algorithm to find the nth ugly number. The first 10 ugly numbers are 1, 2, 3, 4, 5, 6, 8, 9, 10, 12…

class Solution {
public:
    /*
     * @param n an integer
     * @return the nth prime number as description.
     */
    int nthUglyNumber(int n) {
        // write your code here

        vector<int> ugly(n,0);
        ugly[0]=1;
        int ugly2=0,ugly3=0,ugly5=0;

        int i=1;
        while(i<=n-1){
            int minUgly=min(min(ugly[ugly2]*2,ugly[ugly3]*3),ugly[ugly5]*5);
            ugly[i]=minUgly;

            /*注意这里分别if,因为有可能有多个等于minUgly*/
            if(minUgly==ugly[ugly2]*2){
                ugly2++;
            }
            if(minUgly==ugly[ugly3]*3){
                ugly3++;
            }
            if(minUgly==ugly[ugly5]*5){
                ugly5++;
            }
            i++;
        }

        return ugly[n-1];
    }
};