017. Letter Combinations of a Phone Number (电话号码的字母组合) (java)

Author: bluesword12350

solution/017. Letter Combinations of a Phone Number/Solution.java

@@ -0,0 +1,30 @@
+class Solution {
+    public List<String> letterCombinations(String digits) {
+        char[] cs = digits.toCharArray();
+        List<String> result = new ArrayList<>();
+        for (char a : cs) {
+            char[] charArray;
+            switch (a) {
+                case '2': charArray = new char[]{'a','b','c'}; break;
+                case '3': charArray = new char[]{'d','e','f'}; break;
+                case '4': charArray = new char[]{'g','h','i'}; break;
+                case '5': charArray = new char[]{'j','k','l'}; break;
+                case '6': charArray = new char[]{'m','n','o'}; break;
+                case '7': charArray = new char[]{'p','q','r','s'}; break;
+                case '8': charArray = new char[]{'t','u','v'}; break;
+                case '9': charArray = new char[]{'w','x','y','z'}; break;
+                default: return null;
+            }
+            if (result.size() == 0) {
+                for (char aCharArray : charArray) result.add(String.valueOf(aCharArray));
+            } else {
+                List<String> cache = new ArrayList<>();
+                for (String string : result) {
+                    for (char aCharArray : charArray) cache.add(string + aCharArray);
+                }
+                result = cache;
+            }
+        }
+        return result;
+    }
+}