Create firstDuplicate.py

Author: kanglicheng

CodeFights/Interview_Practice/firstDuplicate.py

@@ -0,0 +1,25 @@
+
+#my first solution
+def firstDuplicate(a):
+    d= {}
+    for s in a:
+        if s not in d:
+            d[s]=1
+        else:
+            return s
+    return -1
+
+def firstDuplicate(a):
+    mySet=set()
+    for el in a:
+        if el in mySet:
+            return el
+        mySet.add(el)
+    return -1
+
+def firstDuplicate(a):
+    for i in a:
+        a[abs(i)-1] *= -1
+        if a[abs(i)-1] > 0:
+            return abs(i)
+    return -1