fd

Author: liwentian

doc/Summary.md

@@ -12,4 +12,6 @@
 
  # BackTracking
  - **10. Regular Expression Matching**
+ - **17. Letter Combinations of a Phone Number**
+ - **22. Generate Parentheses**
 

google/RECORDS.md

@@ -5,6 +5,8 @@
 261. Graph Valid Tree
 323. Number of Connected Components in an Undirected Graph
 10. Regular Expression Matching
+17. Letter Combinations of a Phone Number
+22. Generate Parentheses
 
 2017-9-2
 329. Longest Increasing Path in a Matrix

google/src/main/java/com/leetcode/google/GenerateParentheses.java

@@ -0,0 +1,29 @@
+package com.leetcode.google;
+
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * Created by liwentian on 2017/9/3.
+ */
+
+public class GenerateParentheses {
+
+    public List<String> generateParenthesis(int n) {
+        List<String> result = new LinkedList<String>();
+        dfs(result, n, "", 0, 0);
+        return result;
+    }
+
+    private void dfs(List<String> result, int n, String str, int left, int right) {
+        if (left == n && right == n) {
+            result.add(str);
+            return;
+        }
+        if (left > n || right > n || left < right) {
+            return;
+        }
+        dfs(result, n, str + "(", left + 1, right);
+        dfs(result, n, str + ")", left, right + 1);
+    }
+}

google/src/main/java/com/leetcode/google/LetterCombinationsOfAPhoneNumber.java

@@ -0,0 +1,36 @@
+package com.leetcode.google;
+
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * Created by liwentian on 2017/9/3.
+ */
+
+public class LetterCombinationsOfAPhoneNumber {
+
+    final String[] NUMS = {
+            "", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"
+    };
+
+    public List<String> letterCombinations(String digits) {
+        List<String> result = new LinkedList<>();
+        if (digits.isEmpty()) {
+            return result;
+        }
+        dfs(digits, result, 0, "");
+        return result;
+    }
+
+    private void dfs(String digits, List<String> result, int idx, String cur) {
+        if (idx == digits.length()) {
+            result.add(cur);
+            return;
+        }
+
+        int n = digits.charAt(idx) - '0';
+        for (char c : NUMS[n].toCharArray()) {
+            dfs(digits, result, idx + 1, cur + c);
+        }
+    }
+}

solution/src/main/java/com/inuker/solution/GenerateParentheses.java

@@ -13,22 +13,20 @@ public class GenerateParentheses {
     // 耗时4ms
     public List<String> generateParenthesis(int n) {
         List<String> result = new LinkedList<String>();
-        generateParenthesis(result, "", n, 0);
+        dfs(result, n, "", 0, 0);
         return result;
     }
 
-    private void generateParenthesis(List<String> result, String str, int left, int right) {
-        if (left < 0 || right < 0) {
+    private void dfs(List<String> result, int n, String str, int left, int right) {
+        if (left == n && right == n) {
+            result.add(str);
             return;
         }
-
-        if (left == 0 && right == 0) {
-            result.add(str);
+        if (left > n || right > n || left < right) {
             return;
         }
-
-        generateParenthesis(result, str + "(", left - 1, right + 1);
-        generateParenthesis(result, str + ")", left, right - 1);
+        dfs(result, n, str + "(", left + 1, right);
+        dfs(result, n, str + ")", left, right + 1);
     }
 
     // 耗时38ms

test/src/main/java/com/example/Main.java

@@ -1,6 +1,7 @@
 package com.example;
 
 import com.leetcode.google.DecodeString;
+import com.leetcode.google.GenerateParentheses;
 import com.leetcode.google.MissingRanges;
 import com.leetcode.google.QueueReconstructionByHeight;
 import com.leetcode.google.SentenceScreenFitting;
@@ -23,27 +24,10 @@
 public class Main {
 
     public static void main(String[] args) {
-        HashMap<String, String> map = new HashMap<>();
-        map.put("one", null);
-        map.put("two", "japan");
-        map.put("three", "france");
-
-        map.replaceAll(new BiFunction<String, String, String>() {
-            @Override
-            public String apply(String s, String s2) {
-                return null;
-            }
-        });
-
-
-        map.forEach(new BiConsumer<String, String>() {
-            @Override
-            public void accept(String s, String s2) {
-                System.out.println(s + ", " + s2);
-            }
-        });
-
-
+        List<String> lists = new GenerateParentheses().generateParenthesis(3);
+        for (String s : lists) {
+            System.out.println(s);
+        }
 
     }