feat : contains duplicate

Author: ekgns33

contains-duplicate/ekgns33.java

@@ -0,0 +1,49 @@
+import java.util.HashSet;
+import java.util.Set;
+
+/*
+start 7:06~7:14 PASS
+input : integer array
+output : return if input contains duplicate
+constraint : 
+1) empty array?
+    nope. at least one 
+2) size?
+    [1, 10^5]
+3) sorted?
+    nope.
+4) range of elements in the array?
+    [-10^9, 10^9] >> max 2 * 10*9 +1
+
+brute force:
+ds : array. algo : just nested for-loop
+iterate through the array, for index i 0 to n. n indicates the size of input
+    nested loop fo r index j from i+1 to n
+        if nums[j] == nums[i] return true;
+
+return false;
+
+time : O(n^2), space : O(1)
+
+better:
+ds : hashset. algo : one for-loop
+iterate through the array:
+    if set contains current value:
+        return true;
+    else
+        add current value to set
+
+return false;
+time : O(n) space :O(n) 
+
+ */
+class Solution {
+  public boolean containsDuplicate(int[] nums) {
+    Set<Integer> set = new HashSet<>();
+    for(int num : nums) {
+      if(set.contains(num)) return true;
+      set.add(num);
+    }
+    return false;
+  }
+}