Create missing-number.java

Author: GouravRusiya30

Java/missing-number.java

@@ -0,0 +1,24 @@
+/**
+* Time Complexity - O(n)
+* Space Complexity - O(1)
+*
+* Using sum of first n natural numbers formula.
+*/
+class Solution {
+ public int missingNumber(int[] nums) {
+ int numsLen = nums.length;
+ 
+ // sum of n natural number is
+ // Sn = n * (n+1)/2
+ int expectedSum = numsLen*(numsLen+1)/2;
+ 
+ // calculate actual sum
+ int actualSum = 0;
+ for (int i=0; i<numsLen; i++){
+ actualSum += nums[i];
+ }
+ 
+ // subtract actualSum from expectedSum
+ return expectedSum-actualSum;
+ }
+}