Competitive-Coding-1 Complete

Problem1.java

@@ -1 +1,37 @@
+// Find missing number in a sorted array with numbers in range of 1 to N.
+// Time Complexity : O(logN)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : Yes
+// Any problem you faced while coding this : No
+class Solution {
+    public int search(int[] arr) {
+        int left = 0;
+        int right = arr.length - 1;
+        while (left <= right) {
+            int mid = left + (right - left) / 2;
+            // The number at an index should be equal to index + 1
+            if (arr[mid] != mid + 1) {
+                // Missing number is in the left side of mid
+                right = mid - 1;
+            } else {
+                // Missing number is in the right side of mid
+                left = mid + 1;
+            }
+        }
+        // Left pointer always stops at the index where missing number should be.
+        // Number at the index should be index + 1.
+        return left + 1; 
+    }
 
+    public static void main(String[] args) {
+        Solution ob = new Solution();
+        int[] arr = new int[] {1, 2, 3, 5, 6, 7, 8};
+        System.out.println(ob.search(arr)); // returns 4
+        int[] arr1 = new int[] {1, 2, 4, 5, 6, 7, 8, 9};
+        System.out.println(ob.search(arr1)); // retuns 3
+        int[] arr3 = new int[] {2, 3, 4, 5, 6, 7, 8, 9};
+        System.out.println(ob.search(arr3)); // returns 1
+        int[] arr4 = new int[] {1, 2, 3, 4, 5, 6, 7, 8};
+        System.out.println(ob.search(arr4)); // returns 9
+    }
+}