add mathutil

Author: maxxbw

Diff for: lib/utils/MathUtil.java

@@ -0,0 +1,15 @@
+package javaToolkit.lib.utils;
+
+import java.math.BigInteger;
+
+public class MathUtil {
+
+	public static BigInteger binomial(int N, int K) {
+		BigInteger ret = BigInteger.ONE;
+		for (int k = 0; k < K; k++) {
+			ret = ret.multiply(BigInteger.valueOf(N - k)).divide(BigInteger.valueOf(k + 1));
+		}
+		return ret;
+	}
+
+}

Diff for: lib/utils/RandomUtil.java

@@ -1,42 +1,97 @@
 package javaToolkit.lib.utils;
 
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Random;
+import java.util.Set;
 
 public class RandomUtil {
 
-    public Object getARandomElement(List<?> givenList) {
-        Random rand = new Random();
-        Object randomElement = givenList.get(rand.nextInt(givenList.size()));
-        return randomElement;
-    }
+	public Object getARandomElement(List<?> givenList) {
+		Random rand = new Random();
+		Object randomElement = givenList.get(rand.nextInt(givenList.size()));
+		return randomElement;
+	}
 
+	public List<Object> randomSelectWithRepeat(List<Object> givenList, int numberOfElements) {
+		Random rand = new Random();
+		List<Object> selectedEles = new ArrayList<>();
 
-    public List<Object> randomSelectWithRepeat(List<Object> givenList, int numberOfElements) {
-        Random rand = new Random();
-        List<Object> selectedEles = new ArrayList<>();
+		for (int i = 0; i < numberOfElements; i++) {
+			int randomIndex = rand.nextInt(givenList.size());
+			Object randomElement = givenList.get(randomIndex);
+			selectedEles.add(randomElement);
+		}
 
-        for (int i = 0; i < numberOfElements; i++) {
-            int randomIndex = rand.nextInt(givenList.size());
-            Object randomElement = givenList.get(randomIndex);
-            selectedEles.add(randomElement);
-        }
+		return selectedEles;
+	}
 
-        return selectedEles;
-    }
+	public List<?> randomSelectWithoutRepeat(List<?> givenList, int numberOfElements) {
+		Random rand = new Random();
+		List<Object> selectedEles = new ArrayList<>();
 
-    public List<?> randomSelectWithoutRepeat(List<?> givenList, int numberOfElements) {
-        Random rand = new Random();
-        List<Object> selectedEles = new ArrayList<>();
+		for (int i = 0; i < numberOfElements; i++) {
+			int randomIndex = rand.nextInt(givenList.size());
+			Object randomElement = givenList.get(randomIndex);
+			selectedEles.add(randomElement);
+			givenList.remove(randomIndex);
+		}
 
-        for (int i = 0; i < numberOfElements; i++) {
-            int randomIndex = rand.nextInt(givenList.size());
-            Object randomElement = givenList.get(randomIndex);
-            selectedEles.add(randomElement);
-            givenList.remove(randomIndex);
-        }
+		return selectedEles;
+	}
+
+	/**
+	 * include max and min
+	 * 
+	 * @param min
+	 * @param max
+	 * @param k
+	 * @return
+	 */
+	public static Set<Integer> randomGenerateKDistinctNumbers(int min, int max, int k) {
+		Random rand = new Random();
+		Set<Integer> selectedEles = new HashSet<>();
+
+		if (max - min < k) {
+			System.out.printf("Cannot generate %s between %s and %s\n", k, min, max);
+			System.exit(0);
+		}
+
+		while (selectedEles.size() < k) {
+			int randomNum = rand.nextInt((max - min) + 1) + min;
+			selectedEles.add(randomNum);
+		}
+
+		return selectedEles;
+	}
+
+	/**
+	 * include max and min, not contain
+	 * 
+	 * @param min
+	 * @param max
+	 * @param k
+	 * @return
+	 * @throws Exception 
+	 */
+	public static Set<Integer> randomKDistinctNumsWithoutSpecificNum(int min, int max, int k, int withoutNum) throws Exception {
+		Random rand = new Random();
+		Set<Integer> selectedEles = new HashSet<>();
+
+		if (max - min < k) {
+			System.out.printf("Cannot generate %s between %s and %s\n", k, min, max);
+			throw new Exception("Cannot generate " + k + " between " + min + " and " + max + "\n");
+		}
+
+		while (selectedEles.size() < k) {
+			int randomNum = rand.nextInt((max - min) + 1) + min;
+			if (randomNum != withoutNum) {
+				selectedEles.add(randomNum);
+			}
+		}
+
+		return selectedEles;
+	}
 
-        return selectedEles;
-    }
 }