Update README.md

Author: soapyigu

README.md

@@ -18,6 +18,7 @@
 ## Array
 | Title | Solution | Difficulty | Time | Space |
 | ----- | -------- | ---------- | ---- | ----- |
+[Summary Ranges](https://leetcode.com/problems/summary-ranges/)| [Swift](./Array/SummaryRanges.swift)| Medium| O(n)| O(n)|
 [Contains Duplicate](https://leetcode.com/problems/contains-duplicate/)| [Swift](./Array/ContainsDuplicate.swift)| Easy| O(n)| O(n)|
 [Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/)| [Swift](./Array/ContainsDuplicateII.swift)| Easy| O(n)| O(n)|
 [Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/)| [Swift](./Array/RemoveDuplicatesFromSortedArray.swift)| Easy| O(n)| O(1)|
@@ -26,6 +27,7 @@
 [Remove Element](https://leetcode.com/problems/remove-element/)| [Swift](./Array/RemoveElement.swift)| Easy| O(n)| O(1)|
 [Two Sum](https://leetcode.com/problems/two-sum/)| [Swift](./Array/TwoSum.swift)| Easy| O(n)| O(n)|
 [3Sum](https://leetcode.com/problems/3sum/)| [Swift](./Array/ThreeSum.swift)| Medium| O(n^2)| O(n)|
+[4Sum](https://leetcode.com/problems/4sum/)| [Swift](./Array/FourSum.swift)| Medium| O(n^3)| O(n)|
 [Maximum Size Subarray Sum Equals k](https://leetcode.com/problems/maximum-size-subarray-sum-equals-k/)| [Swift](./Array/MaximumSizeSubarraySumEqualsK.swift)| Easy| O(n)| O(n)|
 [Product of Array Except Self](https://leetcode.com/problems/product-of-array-except-self/)| [Swift](./Array/ProductExceptSelf.swift)| Medium| O(n)| O(n)|
 [Rotate Array](https://leetcode.com/problems/rotate-array/)| [Swift](./Array/RotateArray.swift)| Easy| O(n)| O(1)|