feat : missing-number

Author: ekgns33

missing-number/ekgns33.java

@@ -0,0 +1,35 @@
+/**
+ input : integer of array
+ output : return the only missing number
+ constraints:
+ 1) is there any duplicate?
+ no.
+ 2) range of element
+ [0, n]
+
+ solution 1)
+ iterate through the array
+ save to hash set
+ iterate i from 0 to n
+ check if exists
+
+ tc : O(n) sc : O(n)
+
+ solution 2)
+ iterate throught the array
+ add all the elements
+ get sum of integer sequence 0 .. n with. n(n+1)/2
+ get subtraction
+ tc : O(n) sc : O(1)
+ */
+class Solution {
+  public int missingNumber(int[] nums) {
+    int sum = 0;
+    int n = nums.length;
+    for(int num : nums) {
+      sum += num;
+    }
+    int totalSum = (n+1) * n / 2;
+    return totalSum - sum;
+  }
+}