algorithm001
diff --git a/Week_04/id_31/LeetCode_211_031.swift b/Week_04/id_31/LeetCode_211_031.swift
@@ -0,0 +1,53 @@
+//
+//  LeetCode_211_031.swift
+//  TestCoding
+//
+//  Created by 龚欢 on 2019/5/16.
+//  Copyright © 2019 龚欢. All rights reserved.
+//
+
+import Foundation
+
+class WordDictionary {
+    private class TrieNode {
+        var children: [Character: TrieNode] = [:]
+        var isEnd = false
+    }
+
+    private let root: TrieNode
+
+    init() {
+        root = TrieNode()
+    }
+
+    func addWord(_ word: String) {
+        var node = root
+        for char in word {
+            if node.children[char] == nil {
+                node.children[char] = TrieNode()
+            }
+            node = node.children[char]!
+        }
+        node.isEnd = true
+    }
+
+    func search(_ word: String) -> Bool {
+        return bfs(self.root, Array(word), 0)
+    }
+
+    private func bfs(_ node: TrieNode, _ chars: [Character], _ nextIndex: Int) -> Bool {
+        if nextIndex == chars.count {
+            return node.isEnd
+        }
+
+        for (nextChar, nextNode) in node.children {
+            if chars[nextIndex] == "." || chars[nextIndex] == nextChar {
+                if bfs(nextNode, chars, nextIndex + 1) {
+                    return true
+                }
+            }
+        }
+
+        return false
+    }
+}
diff --git a/Week_04/id_31/LeetCode_746_031.swift b/Week_04/id_31/LeetCode_746_031.swift
@@ -0,0 +1,22 @@
+//
+//  LeetCode_746_031.swift
+//  TestCoding
+//
+//  Created by 龚欢 on 2019/5/20.
+//  Copyright © 2019 龚欢. All rights reserved.
+//
+
+import Foundation
+
+class Solution {
+    func minCostClimbingStairs(_ cost: [Int]) -> Int {
+        guard cost.count >= 2 else { return 0 }
+        var dp: [Int: Int] = [:]
+        dp[0] = cost[0]
+        dp[1] = cost[1]
+        for i in 2..<cost.count {
+            dp[i] = min(dp[i-1]!, dp[i-2]!) + cost[i]
+        }
+        return min(dp[cost.count - 1]!, dp[cost.count - 2]!)
+}
+