added all single number solution by c++

cpp/single_numberI.cpp

@@ -0,0 +1,11 @@
+class Solution {
+public:
+    int singleNumber(vector<int>& nums) {
+        int xorsum=0;
+        int n= nums.size();
+        for(int i=0; i<n; i++)
+            xorsum = xorsum ^ nums[i];
+
+        return xorsum;
+    }
+};

cpp/single_numberII.cpp

@@ -0,0 +1,17 @@
+class Solution {
+public:
+    int singleNumber(vector<int>& nums) {
+
+        int res = 0;
+        for(int i=0; i<32; i++)
+        {
+            int mask = (1 << i);
+            int count = 0;
+            for(int j=0; j<nums.size(); j++)
+                if(mask&nums[j]) count++;
+            if(count%3)
+                res |= (1<<i);
+        }
+        return res;
+    }
+};

cpp/single_numberIII.cpp

@@ -0,0 +1,22 @@
+class Solution {
+public:
+    vector<int> singleNumber(vector<int>& nums) {
+        long long int ans=0;
+        for(int i=0; i<nums.size(); i++){
+            ans = ans^nums[i];
+        }
+        int xorr = ans &(~(ans-1));
+        int res1=0,res2=0;
+        for(int i=0;i<nums.size();i++){
+            if(xorr & nums[i]) res1= res1^nums[i];
+            else res2=res2^nums[i];
+        }
+
+        vector<int>v;
+        v.push_back(res1);
+        v.push_back(res2);
+
+        return v;
+    }
+
+};