first commit

MergeSort.java

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+/*
+ * To change this license header, choose License Headers in Project Properties.
+ * To change this template file, choose Tools | Templates
+ * and open the template in the editor.
+ */
+
+/**
+ *
+ * @author lenovo
+ */
+public class MergeSort {
+    
+    private static int[] aux;
+    
+    public static void merge(int[] a, int low, int mid, int high)
+    {
+        int i = low;
+        int j = mid + 1;
+        
+        for(int k=low; k<=high; k++)
+        {
+            aux[k] = a[k];
+        }
+        
+        for(int k=low; k<=high; k++)
+        {
+            if(i>mid)
+            {
+                a[k] = aux[j++];
+            }
+            else if(j > high)
+            {
+                a[k] = aux[i++];
+            }
+            else if (aux[j] < aux[i])
+            {
+                a[k] = aux[j++];
+            }
+            else
+            {
+                a[k] = aux[i++];
+            }
+        }
+    }
+    
+    private static void sort(int[] a, int low, int high)
+    {
+        if(high <= low) return;
+        
+        int mid = low + (high - low) / 2;
+        sort(a, low, mid);
+        sort(a, mid+1, high);
+        merge(a, low, mid, high);
+    }
+    public void sort(int[] a)
+    {
+        int length = a.length;
+        aux = new int[length];
+        sort(a, 0, length-1);
+    }
+}