adding day-four

Author: libterty

README.md

@@ -1,6 +1,7 @@
 # LeetCode Challenge
 
 -   May
-    -   Day 1 [First Bad Version](https://github.com/libterty/leetcode-challenge/blob/master/src/day-one/index.ts)
-    -   Day 2 [Jewels and Stones](https://github.com/libterty/leetcode-challenge/blob/master/src/day-two/index.ts)
-    -   Day 3 [Ransom Note](https://github.com/libterty/leetcode-challenge/blob/master/src/day-three/index.ts)
+    -   Day 1: [First Bad Version](https://github.com/libterty/leetcode-challenge/blob/master/src/day-one/index.ts) :unamused:
+    -   Day 2: [Jewels and Stones](https://github.com/libterty/leetcode-challenge/blob/master/src/day-two/index.ts) :expressionless:
+    -   Day 3: [Ransom Note](https://github.com/libterty/leetcode-challenge/blob/master/src/day-three/index.ts) :hushed:
+    -   Day 4: [Number Complement](https://github.com/libterty/leetcode-challenge/blob/master/src/day-four/index.ts) :laughing:

src/day-four/index.ts

@@ -0,0 +1,15 @@
+/**
+ * @param {number} num
+ * @return {number}
+ */
+export const findComplement = function (num: number): number {
+    let inputStr: string[] = num.toString(2).split('');
+    let outputStr: string = '';
+
+    inputStr.forEach((n: string): string => (n === '1' ? (outputStr += '0') : (outputStr += '1')));
+
+    return parseInt(outputStr, 2);
+};
+
+const data = findComplement(5);
+console.log('data', data);