[Array] Add a solution to Range Sum Query 2D - Immutable

Array/NumMatrix.swift

@@ -0,0 +1,40 @@
+/**
+ * Question Link: https://leetcode.com/problems/range-sum-query-2d-immutable/
+ * Primary idea: Prebuild a sum matrix by original as top left point and current as bottom right point
+ *
+ * Time Complexity: O(mn) for init(), O(1) for sumRegion(), Space Complexity: O(mn)
+ */
+
+class NumMatrix {
+    fileprivate var sum: [[Int]]
+
+    init(_ matrix: [[Int]]) {
+        let m = matrix.count, n = matrix[0].count
+        sum = Array(repeating: Array(repeating: 0, count: n), count: m)
+
+        for i in 0..<m {
+            var lineSum = 0
+            for j in 0..<n {
+                lineSum += matrix[i][j]
+
+                if i == 0 {
+                    sum[i][j] = lineSum
+                } else {
+                    sum[i][j] = lineSum + sum[i - 1][j]
+                }
+            }
+        }
+    }
+
+    func sumRegion(_ row1: Int, _ col1: Int, _ row2: Int, _ col2: Int) -> Int {
+        if row1 == 0 && col1 == 0 {
+            return sum[row2][col2]
+        } else if row1 == 0 {
+            return sum[row2][col2] - sum[row2][col1 - 1]
+        } else if col1 == 0 {
+            return sum[row2][col2] - sum[row1 - 1][col2]
+        } else {
+            return sum[row2][col2] - sum[row2][col1 - 1] - sum[row1 - 1][col2] + sum[row1 - 1][col1 - 1]
+        }
+    }
+}

README.md

@@ -28,7 +28,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 265 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
+[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 266 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
 
 
 ## Array
@@ -54,6 +54,7 @@
 [3Sum Closest](https://leetcode.com/problems/3sum-closest/)| [Swift](./Array/ThreeSum.swift)| Medium| O(n^2)| O(nC3)|
 [4Sum](https://leetcode.com/problems/4sum/)| [Swift](./Array/FourSum.swift)| Medium| O(n^3)| O(nC4)|
 [Summary Ranges](https://leetcode.com/problems/summary-ranges/)| [Swift](./Array/SummaryRanges.swift)| Medium| O(n)| O(n)|
+[Range Sum Query 2D - Immutable](https://leetcode.com/problems/range-sum-query-2d-immutable/)| [Swift](./Array/NumMatrix.swift)| Medium| O(mn)| O(mn)|
 [Asteroid Collision](https://leetcode.com/problems/asteroid-collision/)| [Swift](./Array/AsteroidCollision.swift)| Medium| O(n)| O(n)|
 [Maximize Distance to Closest Person](https://leetcode.com/problems/maximize-distance-to-closest-person/)| [Swift](./Array/MaximizeDistanceToClosestPerson.swift)| Easy| O(n)| O(1)|
 [Exam Room](https://leetcode.com/problems/exam-room/)| [Swift](./Array/ExamRoom.swift)| Medium| O(n)| O(n)|
@@ -537,7 +538,7 @@
 |		|	307	|	[Range Sum Query - Mutable](https://leetcode.com/problems/range-sum-query-mutable/)	|	Medium
 |		|	306	|	[Additive Number](https://leetcode.com/problems/additive-number/)	|	Medium
 |	[Swift](./UnionFind/NumberIslandsII.swift)	|	305	|	[Number of Islands II](https://leetcode.com/problems/number-of-islands-ii/)  ♥	|	Hard
-|		|	304	|	[Range Sum Query 2D - Immutable](https://leetcode.com/problems/range-sum-query-2d-immutable/)	|	Medium
+|	[Swift](./Array/NumMatrix.swift)	|	304	|	[Range Sum Query 2D - Immutable](https://leetcode.com/problems/range-sum-query-2d-immutable/)	|	Medium
 |		|	303	|	[Range Sum Query - Immutable](https://leetcode.com/problems/range-sum-query-immutable/)	| Easy
 |		|	302	|	[Smallest Rectangle Enclosing Black Pixels](https://leetcode.com/problems/smallest-rectangle-enclosing-black-pixels/)  ♥	|	Hard
 |	[Swift](./DFS/RemoveInvalidParentheses.swift)	|	301	|	[Remove Invalid Parentheses](https://leetcode.com/problems/remove-invalid-parentheses/)	|	Hard