new soln: find duplicate, 10.08 (careercup#84)

Author: kapilraghuwanshi

chapter10/10.08 - Find Duplicates/findDuplicates.js

@@ -1,2 +1,49 @@
-// sort numbers
-// stream through numbers and print elements which is a duplicate of the immediate previous number
+// We're given 4 kilobytes (4 * 2^10 * 8 = 32*2^10 bits) of main memory(RAM) to write a program to print all duplicate entries in an array 
+// from 1 to N where N is at most 32,000 (32*2^10).
+
+// We can use an Int8Array that uses 1 Byte per element to store 0's if we haven't seen it and 1's if we have seen it. 
+// The Int8Array typed array represents an array of twos-complement 8-bit signed integers.
+// 4 KB > 32,000 bits
+
+// Time Complexity - O(n)
+// Space Complexity - O(n)
+
+// Let's have a JavaScript Solution of this program:
+
+function FindDuplicates(arr, range = 32000) {
+  // Initialize integer 8 bit array with 0's at every index
+  const numbersSeen = new Int8Array(range);
+  const duplicates = [];
+  for (let i = 0; i < arr.length; i++) {
+    if (numbersSeen[arr[i]] === 0) {
+      numbersSeen[arr[i]] = 1;
+    } else {
+      duplicates.push(arr[i]);
+    }
+  }
+  return duplicates;
+}
+
+ const arr = [
+      0,
+      1,
+      1,
+      2,
+      4,
+      6,
+      7,
+      9,
+      9,
+      34,
+      56,
+      78,
+      90,
+      101,
+      345,
+      789,
+      999,
+      999,
+      11000
+    ];
+    FindDuplicates(arr);
+// [1, 9, 999]