diff --git a/README.md b/README.md
index bb333dc26..d1f31633c 100644
--- a/README.md
+++ b/README.md
@@ -82,6 +82,7 @@ LeetCode
 |1464|[Maximum Product of Two Elements in an Array](https://leetcode.com/problems/maximum-product-of-two-elements-in-an-array/) | [C++](./algorithms/cpp/maximumProductOfTwoElementsInAnArray/MaximumProductOfTwoElementsInAnArray.cpp)|Easy|
 |1460|[Make Two Arrays Equal by Reversing Sub-arrays](https://leetcode.com/problems/make-two-arrays-equal-by-reversing-sub-arrays/) | [C++](./algorithms/cpp/twoArraysEqualByReversingSubArrays/MakeTwoArraysEqualByReversingSubArrays.cpp)|Easy|
 |1376|[Time Needed to Inform All Employees](https://leetcode.com/problems/time-needed-to-inform-all-employees/) | [C++](./algorithms/cpp/timeNeededToInformAllEmployees/TimeNeededToInformAllEmployees.cpp)|Medium|
+|1375|[Bulb Switcher III](https://leetcode.com/problems/bulb-switcher-iii) | [C++](./algorithms/cpp/bulbSwitcher/BulbSwitcher.III.cpp)|Medium|
 |1353|[Maximum Number of Events That Can Be Attended](https://leetcode.com/problems/maximum-number-of-events-that-can-be-attended/) | [C++](./algorithms/cpp/maximumNumberOfEventsThatCanBeAttended/MaximumNumberOfEventsThatCanBeAttended.cpp)|Medium|
 |1333|[Filter Restaurants by Vegan-Friendly, Price and Distance](https://leetcode.com/problems/filter-restaurants-by-vegan-friendly-price-and-distance/) | [C++](./algorithms/cpp/filterRestaurantsByVeganFriendlyPriceAndDistance/FilterRestaurantsByVeganFriendlyPriceAndDistance.cpp)|Medium|
 |1207|[Unique Number of Occurrences](https://leetcode.com/problems/unique-number-of-occurrences/) | [C++](./algorithms/cpp/uniqueNumberOfOccurrences/Unique-Number-of-Occurrences.cpp)|Easy|
diff --git a/algorithms/cpp/bulbSwitcher/BulbSwitcher.II.cpp b/algorithms/cpp/bulbSwitcher/BulbSwitcher.II.cpp
index 8ed85cb67..55d375115 100644
--- a/algorithms/cpp/bulbSwitcher/BulbSwitcher.II.cpp
+++ b/algorithms/cpp/bulbSwitcher/BulbSwitcher.II.cpp
@@ -1,4 +1,4 @@
-// Source : https://leetcode.com/problems/bulb-switcher-ii/submissions/
+// Source : https://leetcode.com/problems/bulb-switcher-ii/
 // Author : Hao Chen
 // Date   : 2021-03-29
 
diff --git a/algorithms/cpp/bulbSwitcher/BulbSwitcher.III.cpp b/algorithms/cpp/bulbSwitcher/BulbSwitcher.III.cpp
new file mode 100644
index 000000000..91e8bc9c0
--- /dev/null
+++ b/algorithms/cpp/bulbSwitcher/BulbSwitcher.III.cpp
@@ -0,0 +1,67 @@
+// Source : https://leetcode.com/problems/bulb-switcher-iii
+// Author : Hao Chen
+// Date   : 2021-03-29
+
+/***************************************************************************************************** 
+ *
+ * There is a room with n bulbs, numbered from 1 to n, arranged in a row from left to right. 
+ * Initially, all the bulbs are turned off.
+ * 
+ * At moment k (for k from 0 to n - 1), we turn on the light[k] bulb. A bulb change color to blue only 
+ * if it is on and all the previous bulbs (to the left) are turned on too.
+ * 
+ * Return the number of moments in which all turned on bulbs are blue.
+ * 
+ * Example 1:
+ * 
+ * Input: light = [2,1,3,5,4]
+ * Output: 3
+ * Explanation: All bulbs turned on, are blue at the moment 1, 2 and 4.
+ * 
+ * Example 2:
+ * 
+ * Input: light = [3,2,4,1,5]
+ * Output: 2
+ * Explanation: All bulbs turned on, are blue at the moment 3, and 4 (index-0).
+ * 
+ * Example 3:
+ * 
+ * Input: light = [4,1,2,3]
+ * Output: 1
+ * Explanation: All bulbs turned on, are blue at the moment 3 (index-0).
+ * Bulb 4th changes to blue at the moment 3.
+ * 
+ * Example 4:
+ * 
+ * Input: light = [2,1,4,3,6,5]
+ * Output: 3
+ * 
+ * Example 5:
+ * 
+ * Input: light = [1,2,3,4,5,6]
+ * Output: 6
+ * 
+ * Constraints:
+ * 
+ * 	n == light.length
+ * 	1 <= n <= 5 * 10^4
+ * 	light is a permutation of  [1, 2, ..., n]
+ ******************************************************************************************************/
+
+class Solution {
+public:
+    int numTimesAllBlue(vector<int>& light) {
+        int n = light.size();
+        vector<bool> on(n, false);
+        int left = 0; //tracking the most left place that all bubls are truned on.
+        int result = 0;
+        for(int i=0; i<light.size(); i++){
+            on[light[i]-1] = true;
+            while (left < n && on[left]) left++;
+            //if the bulbs are on left is equal to current bulbs we trun on.
+            //then they all are blue.
+            if (left == i+1) result++; 
+        }
+        return result;
+    }
+};