[GangBean] Week 1

contains-duplicate/GangBean.java

@@ -0,0 +1,12 @@
+import java.util.Arrays;
+import java.util.stream.Collectors;
+
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        /***
+            compare length of array and length of set.
+            O(n) given that n is length of array nums
+        */
+        return nums.length > Arrays.stream(nums).boxed().collect(Collectors.toSet()).size();
+    }
+}

valid-palindrome/GangBean.java

@@ -0,0 +1,20 @@
+class Solution {
+    public boolean isPalindrome(String s) {
+        /**
+         * Step 1: Convert the input string to lowercase. -> O(n)
+         * Step 2: Remove all non-alphanumeric characters using regex. -> O(n)
+         * Step 3: Use two pointers to compare characters from both ends of the string. -> O(n)
+         * Total time complexity: O(n), where n is the length of the string.
+         */
+        s = s.toLowerCase();
+        s = s.replaceAll("[^a-z0-9]", "");
+        int left = 0;
+        int right = s.length() - 1;
+        if (right <= 0) return true;
+        while (left < right) {
+            if (s.charAt(left++) != s.charAt(right--)) return false;
+        }
+        return true;
+    }
+}
+