update 679

fishercoder1534 · fishercoder1534 · commit 2ca644d1cbc1 · 2017-09-18T08:04:04.000-07:00
diff --git a/README.md b/README.md
@@ -23,7 +23,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |  #  |      Title     |   Solutions   | Time          | Space         | Difficulty  | Tag          | Notes
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
 |680|[Valid Palindrome II](https://leetcode.com/problems/valid-palindrome-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_680.java) | O(n) | O(1) | Easy | String
-|679|[24 Game](https://leetcode.com/problems/24-game/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_679.java) | O(n^2) | O(n) | Hard | Recursion
+|679|[24 Game](https://leetcode.com/problems/24-game/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_679.java) | O(1) (Upper bound 9216)| O(1) | Hard | Recursion
 |678|[Valid Parenthesis String](https://leetcode.com/problems/valid-parenthesis-string/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_678.java) | O(n) | O(1) | Medium| Recursion, Greedy
 |677|[Map Sum Pairs](https://leetcode.com/problems/map-sum-pairs/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_677.java) | O(n) | O(n) | Medium | HashMap
 |676|[Implement Magic Dictionary](https://leetcode.com/problems/implement-magic-dictionary/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_676.java) | O(n^2) | O(n) | Medium |
diff --git a/src/main/java/com/fishercoder/solutions/_679.java b/src/main/java/com/fishercoder/solutions/_679.java
@@ -27,6 +27,10 @@
 
 public class _679 {
     public static class Solution1 {
+        /**Since there are only 4 cards and only 4 operations, we can iterate through all possible combinations, there's a total of 9216 possibilities:
+         * 1. we pick two out of four cards, with order (since order matters for division), 4 * 3 = 12, then pick one of four operations: 12 * 4 = 48;
+         * 2. then we pick two from these three numbers: 12 * 4 * 3 * 4 * 2 = 1152
+         * 3. then we pick the remaining two: 1152 * 2 * 4 = 9216 (with order and out of 4 operations)*/
         public boolean judgePoint24(int[] nums) {
             return dfs(IntStream.of(nums).mapToDouble(num -> num).toArray());
         }
