java: add «151. Reverse Words in a String»

Signed-off-by: Matej Focko <me@mfocko.xyz>

java/reverse-words-in-a-string.java

@@ -0,0 +1,16 @@
+class Solution {
+  private static <T> void reverse(T[] arr) {
+    for (int l = 0, r = arr.length - 1; l < r; ++l, --r) {
+      var tmp = arr[l];
+      arr[l] = arr[r];
+      arr[r] = tmp;
+    }
+  }
+
+  public String reverseWords(String s) {
+    String[] words = s.strip().split("\\s+");
+    reverse(words);
+
+    return String.join(" ", words);
+  }
+}