[Array] Use Binary search to check whether num is perfect squares

README.md

@@ -227,7 +227,6 @@
 [Longest Increasing Subsequence](https://leetcode.com/problems/longest-increasing-subsequence/)| [Swift](./DP/LongestIncreasingSubsequence.swift)| Medium| O(nlogn)| O(n)|
 [Palindromic Substrings](https://leetcode.com/problems/palindromic-substrings/)| [Swift](./DP/PalindromicSubstrings.swift)| Medium| O(n^2)| O(n^2)|
 [Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/)| [Swift](./DP/LongestPalindromicSubstring.swift)| Medium| O(n^2)| O(n^2)|
-[Perfect Squares](https://leetcode.com/problems/perfect-squares/)| [Swift](./DP/PerfectSquares.swift)| Medium| O(n^2)| O(n)|
 [House Robber](https://leetcode.com/problems/house-robber/)| [Swift](./DP/HouseRobber.swift)| Easy| O(n)| O(1)|
 [House Robber II](https://leetcode.com/problems/house-robber-ii/)| [Swift](./DP/HouseRobberII.swift)| Medium| O(n)| O(1)|
 [Paint Fence](https://leetcode.com/problems/paint-fence/)| [Swift](./DP/PaintFence.swift)| Easy| O(n)| O(n)|
@@ -343,6 +342,7 @@
 [Sqrt(x)](https://leetcode.com/problems/sqrtx/)| [Swift](./Search/Sqrtx.swift)| Medium| O(logn)| O(1)|
 [Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/)| [Swift](./Search/MedianTwoSortedArrays.swift)| Hard| O(log(m + n))| O(1)|
 [Minimize Max Distance to Gas Station](https://leetcode.com/problems/minimize-max-distance-to-gas-station/)| [Swift](./Search/MinimizeMaxDistanceGasStation.swift)| Hard| O(nlogm)| O(1)|
+[Perfect Squares](https://leetcode.com/problems/perfect-squares/)| [Swift](./Search/PerfectSquares.swift)| Medium| O(logn)| O(1)|
 
 ## Sort
 | Title | Solution | Difficulty | Time | Space |

Search/PerfectSquares.swift

@@ -0,0 +1,29 @@
+/**
+ * Question Link: https://leetcode.com/problems/perfect-squares/
+ * Primary idea: Binary Search, base on the num itself, from 0 to num, divide the search by half each time  
+ *               
+ * Time Complexity: O(logn), Space Complexity: O(1)
+ */
+
+class PerfectSquares {
+    func numSquares(n: Int) -> Int {
+        if num == 1 {
+            return true 
+        }
+
+        var l = 0, r = num / 2 
+        while l <= r {
+            let mid = l + (r - l) / 2
+            let tmp = mid * mid 
+            if tmp == num {
+                return true 
+            } else if tmp < num {
+                l = mid + 1
+            } else {
+                r = mid - 1
+            }
+        }
+
+        return false
+    }
+}