add day-nine

Author: libterty

README.md

@@ -9,3 +9,4 @@
     -   Day 6: [Majority Element](https://github.com/libterty/leetcode-challenge/blob/master/src/may/day-six/index.ts) :relaxed:
     -   Day 7: [Cousins in Binary Tree](https://github.com/libterty/leetcode-challenge/blob/master/src/may/day-seven/index.ts) :hushed:
     -   Day 8: [check Straight Line](https://github.com/libterty/leetcode-challenge/blob/master/src/may/day-eight/index.ts) :grin:
+    -   Day 9: [Is Perfect Square](https://github.com/libterty/leetcode-challenge/blob/master/src/may/day-nine/index.ts) :alien:

src/may/day-nine/index.ts

@@ -0,0 +1,25 @@
+/*
+ *
+ * isPerfectSquare
+ * @param {number} num
+ * @return {boolean}
+ */
+
+//Note: Do not use any built-in library function such as sqrt.
+export const isPerfectSquare = function (num: number): boolean {
+    if (num === 0) return false;
+    if (num === 1) return true;
+    let i: number = 1;
+    let result: number = 1;
+    while (result < num) {
+        i++;
+        result = i * i;
+    }
+    return result === num;
+};
+
+const a = isPerfectSquare(16);
+const b = isPerfectSquare(14);
+
+console.log('a', a);
+console.log('b', b);