Java solution 313

Author: gavinfish

java/_313SuperUglyNumber.java

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+/**
+ * Write a program to find the nth super ugly number.
+ * <p>
+ * Super ugly numbers are positive numbers whose all prime factors are in the given prime list primes of size k. For
+ * example, [1, 2, 4, 7, 8, 13, 14, 16, 19, 26, 28, 32] is the sequence of the first 12 super ugly numbers given
+ * primes = [2, 7, 13, 19] of size 4.
+ * <p>
+ * Note:
+ * (1) 1 is a super ugly number for any given primes.
+ * (2) The given numbers in primes are in ascending order.
+ * (3) 0 < k ≤ 100, 0 < n ≤ 106, 0 < primes[i] < 1000.
+ * (4) The nth super ugly number is guaranteed to fit in a 32-bit signed integer.
+ * <p>
+ * Credits:
+ * Special thanks to @dietpepsi for adding this problem and creating all test cases.
+ * <p>
+ * Created by drfish on 16/06/2017.
+ */
+public class _313SuperUglyNumber {
+    public int nthSuperUglyNumber(int n, int[] primes) {
+        int[] indexes = new int[primes.length];
+        int[] superUgly = new int[n];
+
+        superUgly[0] = 1;
+        for (int i = 1; i < n; i++) {
+            superUgly[i] = Integer.MAX_VALUE;
+            for (int j = 0; j < primes.length; j++) {
+                superUgly[i] = Math.min(superUgly[i], primes[j] * superUgly[indexes[j]]);
+            }
+            for (int j = 0; j < primes.length; j++) {
+                while (primes[j] * superUgly[indexes[j]] <= superUgly[i]) {
+                    indexes[j]++;
+                }
+            }
+        }
+        return superUgly[n - 1];
+    }
+
+    public static void main(String[] args) {
+        _313SuperUglyNumber solution = new _313SuperUglyNumber();
+        assert 32 == solution.nthSuperUglyNumber(12, new int[]{2, 7, 13, 19});
+    }
+}