add better solution for Combination Sum II in README

Author: P-ppc

algorithms/CombinationSumII/README.md

@@ -1,2 +1,32 @@
 # Combination Sum II
-We can solve this proble by Backtracking Algorithm like [Combination Sum](./CombinationSum)
+We can solve this proble by Backtracking Algorithm like [Combination Sum](./CombinationSum), the better solution is like below:
+```java
+class Solution {
+    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
+        List<List<Integer>> res = new ArrayList<List<Integer>>();
+        Arrays.sort(candidates);
+        backTrack(0, candidates, new ArrayList<Integer>(), target, res);
+        return res;
+    }
+    
+    public void backTrack(int beg, int[] candidates, List<Integer> temp, int target, List<List<Integer>> res) {
+        if (target == 0) {
+            res.add(temp);
+        } else {
+            int i = beg;
+            while (i < candidates.length) {
+                int c = candidates[i];
+                if (c <= target) {
+                    List<Integer> t = new ArrayList<Integer>(temp);
+                    t.add(c);
+                    backTrack(i + 1, candidates, t, target - c, res);
+                    while (i + 1 < candidates.length && candidates[i + 1] == c) {
+                        i++;
+                    }
+                }
+                i++;
+            }
+        }
+    }
+}
+```