/**

public int nthUglyNumber(int n) {

if (n < 7) {

return n;

}

int[] res = new int[n];

// first ugly number.

res[0] = 1;

// use three variable 'two', 'three' and 'five',

// respective represent current minimum haven't use ugly number,

// which will product 2, product 3 and product 5 for gain new ugly number.

int two = 0, three = 0, five = 0;

for (int i = 1; i < n; i++) {

// storage the minimum number in current gained new ugly numbers.

res[i] = Math.min(Math.min(res[two] * 2, res[three] * 3), res[five] * 5);

// move current used ugly number's variable to point the next ugly number.

if (res[i] == res[two] * 2) {

two++;

}

if (res[i] == res[three] * 3) {

three++;

}

if (res[i] == res[five] * 5) {

five++;

}

}

return res[n - 1];

}