Added 1 solution & modified 2 solutions

Author: varunu28

Easy/Flipping an Image.java

@@ -1,22 +1,27 @@
 class Solution {
-	public int[][] flipAndInvertImage(int[][] A) {
-        int[][] ans = new int[A.length][A[0].length];
-        
-        for (int i=0; i<A.length; i++) {
-            List<Integer> temp = Arrays.stream(A[i]).
-            							boxed().
-            							collect(Collectors.toList());
-            
-            Collections.reverse(temp);
-            ans[i] = temp.stream().mapToInt(e -> e).toArray();
-        }
-        
-        for (int i=0;i<ans.length;i++) {
-        	for (int j=0;j<ans[i].length;j++) {
-        		ans[i][j] = ans[i][j] == 1 ? 0 : 1;
-        	}
-        }
-        
-        return ans;
+  public int[][] flipAndInvertImage(int[][] A) {
+    for (int[] arr : A) {
+      reverse(arr);
+      invert(arr);
     }
+    return A;
+  }
+  
+  private void reverse(int[] arr) {
+    int start = 0;
+    int end = arr.length - 1;
+    while (start < end) {
+      int temp = arr[start];
+      arr[start] = arr[end];
+      arr[end] = temp;
+      start++;
+      end--;
+    }
+  }
+  
+  private void invert(int[] arr) {
+    for (int i = 0; i < arr.length; i++) {
+      arr[i] = arr[i] ^ 1;
+    }
+  }
 }

Easy/Last Stone Weight.java

@@ -1,27 +1,20 @@
 class Solution {
-    public int lastStoneWeight(int[] stones) {
-        PriorityQueue<Integer> pq = new PriorityQueue<>(new Comparator<Integer>() {
-            @Override
-            public int compare(Integer o1, Integer o2) {
-                return o2.compareTo(o1);
-            }
-        });
-
-        for (int stone : stones) {
-            pq.add(stone);
-        }
-
-        while (pq.size() > 1) {
-            int stone1 = pq.poll();
-            int stone2 = pq.poll();
-
-            int resSize = Math.max(stone1, stone2) - Math.min(stone1, stone2);
-
-            if (resSize > 0) {
-                pq.add(resSize);
-            }
-        }
-
-        return pq.size() == 1 ? pq.poll() : 0;
+  public int lastStoneWeight(int[] stones) {
+    PriorityQueue<Integer> pq = new PriorityQueue<>(new Comparator<Integer>(){
+      public int compare(Integer o1, Integer o2) {
+        return o2 - o1;
+      }
+    });
+    for (int stone : stones) {
+      pq.add(stone);
     }
+    while(pq.size() > 1) {
+      int y = pq.poll();
+      int x = pq.poll();
+      if (x != y) {
+        pq.add(y - x);
+      }
+    }
+    return pq.isEmpty() ? 0 : pq.poll();
+  }
 }

Easy/Sort Array By Parity II.java

@@ -0,0 +1,16 @@
+class Solution {
+  public int[] sortArrayByParityII(int[] A) {
+    int start = 1;
+    for (int i = 0; i < A.length; i += 2) {
+      if (A[i] % 2 == 1) {
+        while (A[start] % 2 != 0) {
+          start += 2;
+        }
+        int temp = A[i];
+        A[i] = A[start];
+        A[start] = temp;
+      }
+    }
+    return A;
+  }
+}