[DFS] Add a solution to Is Graph Bipartite

DFS/IsGraphBipartite.swift

@@ -0,0 +1,37 @@
+/**
+ * Question Link: https://leetcode.com/problems/is-graph-bipartite/
+ * Primary idea: Depth-first Search, try to color the graph with two colors
+ * 
+ * Time Complexity: O(n), Space Complexity: O(n)
+ *
+ */
+
+class IsGraphBipartite {
+    func isBipartite(_ graph: [[Int]]) -> Bool {
+        var colors = Array(repeating: -1, count: graph.count)
+
+        for i in 0..<graph.count {
+            if colors[i] == -1 && !validColor(&colors, 0, graph, i) {
+                return false
+            }
+        }
+
+        return true
+    }
+
+    fileprivate func validColor(_ colors: inout [Int], _ color: Int, _ graph: [[Int]], _ index: Int) -> Bool {
+        if colors[index] != -1 {
+            return colors[index] == color
+        }
+
+        colors[index] = color
+
+        for neighbor in graph[index] {
+            if !validColor(&colors, 1 - color, graph, neighbor) {
+                return false
+            }
+        }
+
+        return true
+    }
+}

README.md

@@ -28,7 +28,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 243 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 244 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
@@ -223,6 +223,7 @@
 [Factor Combinations](https://leetcode.com/problems/factor-combinations/)| [Swift](./DFS/FactorCombinations.swift)| Medium| O(n^n))| O(2^n - 1)|
 [Generalized Abbreviation](https://leetcode.com/problems/generalized-abbreviation/)| [Swift](./DFS/GeneralizedAbbreviation.swift)| Medium| O(n!)| O(2^n)|
 [Palindrome Partitioning](https://leetcode.com/problems/palindrome-partitioning/)| [Swift](./DFS/PalindromePartitioning.swift)| Medium| O(n!)| O(n)|
+[Is Graph Bipartite](https://leetcode.com/problems/is-graph-bipartite/)| [Swift](./DFS/IsGraphBipartite.swift)| Medium| O(n)| O(n)|
 [Number of Islands](https://leetcode.com/problems/number-of-islands/)| [Swift](./DFS/NumberofIslands.swift)| Medium| O((mn)^2)| O(1)|
 [Walls and Gates](https://leetcode.com/problems/walls-and-gates/)| [Swift](./DFS/WallsGates.swift)| Medium| O(n!)| O(2^n)|
 [Word Search](https://leetcode.com/problems/word-search/)| [Swift](./DFS/WordSearch.swift)| Medium| O((n^2)!)| O(n^2)|