LintCode-Kth Prime Number.

 1 class Solution {
 2     /**
 3      * @param k: The number k.
 4      * @return: The kth prime number as description.
 5      */
 6     public long kthPrimeNumber(int k) {
 7         if (k==0) return 1;
 8         
 9         long[] res = new long[k+1];
10         res[0] = 1;
11         int p3 = 0, p5 = 0, p7 = 0;
12         for (int i=1;i<=k;i++){
13             //find the minimum prime number.
14             long val = Math.min(res[p3]*3, res[p5]*5);
15             val = Math.min(val, res[p7]*7);
16             if (val / res[p3] == 3) p3++;
17             if (val / res[p5] == 5) p5++;
18             if (val / res[p7] == 7) p7++;
19             res[i] = val;
20         }
21         return res[k];
22     }
23 };