319 solved.

Author: liuyubobobo

0319-Bulb-Switcher/cpp-0319/CMakeLists.txt

@@ -0,0 +1,7 @@
+cmake_minimum_required(VERSION 3.5)
+project(cpp_0319)
+
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+
+set(SOURCE_FILES main.cpp)
+add_executable(cpp_0319 ${SOURCE_FILES})

0319-Bulb-Switcher/cpp-0319/main.cpp

@@ -0,0 +1,51 @@
+/// Source : https://leetcode.com/problems/bulb-switcher/description/
+/// Author : liuyubobobo
+/// Time   : 2017-12-01
+
+#include <iostream>
+#include <cassert>
+
+using namespace std;
+
+/// For every number, see whether the divisor number is odd
+/// Time Complexity: O(n*sqrt(n))
+/// Space Complexity: O(1)
+///
+/// Time Limit Exceed!!!
+class Solution {
+
+public:
+    int bulbSwitch(int n) {
+
+        assert(n >= 0);
+
+        if(n <= 1)
+            return n;
+
+        int count = 1;
+        for(int i = 2 ; i <= n ; i ++)
+            if(divisorNumber(i) % 2 == 1)
+                count += 1;
+        return count;
+    }
+
+private:
+    int divisorNumber(int x){
+        int ret = 0;
+        for(int i = 1 ; i * i <= x ; i ++)
+            if(x % i == 0){
+                ret += 1;
+                if(x / i != i)
+                    ret += 1;
+            }
+        return ret;
+    }
+};
+
+int main() {
+
+    cout << Solution().bulbSwitch(2) << endl;
+    cout << Solution().bulbSwitch(3) << endl;
+
+    return 0;
+}

0319-Bulb-Switcher/cpp-0319/main2.cpp

@@ -0,0 +1,29 @@
+/// Source : https://leetcode.com/problems/bulb-switcher/description/
+/// Author : liuyubobobo
+/// Time   : 2017-12-01
+
+#include <iostream>
+#include <cmath>
+#include <cassert>
+
+using namespace std;
+
+/// Only square number have odd divisor number!
+/// Time Complexity: O(1)
+/// Space Complexity: O(1)
+class Solution {
+
+public:
+    int bulbSwitch(int n) {
+        assert(n >= 0);
+        return (int)sqrt(n);
+    }
+};
+
+int main() {
+
+    cout << Solution().bulbSwitch(2) << endl;
+    cout << Solution().bulbSwitch(3) << endl;
+
+    return 0;
+}

readme.md

@@ -134,6 +134,8 @@ email: [[email protected]](mailto:[email protected])
 | 308 | [Range Sum Query 2D - Mutable](https://leetcode.com/problems/range-sum-query-2d-mutable/description/) | | [C++](0308-Range-Sum-Query-2D-Mutable/cpp-0308/) | | |
 | 309 | [Best Time to Buy and Sell Stock with Cooldown](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/description/) | | [C++](0309-Best-Time-to-Buy-and-Sell-Stock-with-Cooldown/cpp-0309/) | | |
 | | | | | | |
+| 319 | [Bulb Switcher](https://leetcode.com/problems/bulb-switcher/description/) | [无] | [C++](0319-Bulb-Switcher/cpp-0319/) | | |
+| | | | | | |
 | 343 | [Integer Break](https://leetcode.com/problems/integer-break/description/) | [无] | [C++](0343-Integer-Break/cpp-0343/) | [Java](0343-Integer-Break/java-0343/src/) | |
 | | | | | | |
 | 347 | [Top K Frequent Elements](https://leetcode.com/problems/top-k-frequent-elements/description/) | [无] | [C++](0347-Top-K-Frequent-Elements/cpp-0347/) | [Java](0347-Top-K-Frequent-Elements/java-0347/src/) | |