Added two Java codes : MeregeSort & QuickSort

DSA/java/MergeSort.java

@@ -0,0 +1,50 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+
+public class MergeSort {
+    public static void main(String[] args) {
+        int[] arr = {5,4,3,2,1};
+        mergeSort(arr,0, arr.length-1);
+        System.out.println(Arrays.toString(arr));
+    }
+
+    static void mergeSort(int[] arr,int low,int high){
+        if(low>=high){
+            return;
+        }
+        int mid  = (low + high)/2;
+        mergeSort(arr,low,mid);
+        mergeSort(arr,mid+1,high);
+        merge(arr,low,mid,high);
+
+    }
+
+    static void merge(int[] arr, int low, int mid, int high) {
+        ArrayList<Integer> ans  = new ArrayList<>();
+        int left  = low;
+        int right = mid+1;
+        while(left<=mid && right <=high){
+            if(arr[left]<=arr[right]){
+                ans.add(arr[left]);
+                left++;
+            }
+            else {
+                ans.add(arr[right]);
+                right++;
+            }
+        }
+        while(left <= mid){
+            ans.add(arr[left]);
+            left++;
+        }
+
+        while(right <= high){
+            ans.add(arr[right]);
+            right++;
+        }
+
+        for (int i = low; i <= high; i++) {
+            arr[i] = ans.get(i - low);
+        }
+    }
+}

DSA/java/QuickSort.java

@@ -0,0 +1,47 @@
+
+
+
+import java.util.Arrays;
+
+public class QuickSort {
+    public static void main(String[] args) {
+        int[] arr = {10,1,3,9,8};
+        sort(arr, 0, arr.length - 1);
+        System.out.println(Arrays.toString(arr));
+    }
+
+    static void sort(int[] nums, int low, int hi) {
+        if (low >= hi) {
+            return;
+        }
+
+        int s = low;
+        int e = hi;
+        int m = s + (e - s) / 2;
+        int pivot = nums[m];
+
+        while (s <= e) {
+
+            // also a reason why if its already sorted it will not swap
+            while (nums[s] < pivot) {
+                s++;
+            }
+
+            while (nums[e] > pivot) {
+                e--;
+            }
+
+            if (s <= e) {
+                int temp = nums[s];
+                nums[s] = nums[e];
+                nums[e] = temp;
+                s++;
+                e--;
+            }
+        }
+
+        // now my pivot is at correct index, please sort two halves now
+        sort(nums, low, e);
+        sort(nums, s, hi);
+    }
+}