New Problem Solution - "1513. Number of Substrings With Only 1s"

README.md

@@ -10,10 +10,12 @@ LeetCode
 | # | Title | Solution | Difficulty |
 |---| ----- | -------- | ---------- |
 |1573|[Number of Ways to Split a String](https://leetcode.com/problems/number-of-ways-to-split-a-string/) | [C++](./algorithms/cpp/NumberOfWaysToSplitString/NumberOfWaysToSplitString.cpp)|Medium|
+|1556|[Thousand Separator](https://leetcode.com/problems/thousand-separator/) | [C++](./algorithms/cpp/thousandSeparator/ThousandSeparator.cpp)|Easy|
 |1551|[Minimum Operations to Make Array Equal](https://leetcode.com/problems/minimum-operations-to-make-array-equal/) | [C++](./algorithms/cpp/minimumOperationsToMakeArrayEqual/MinimumOperationsToMakeArrayEqual.cpp)|Medium|
 |1550|[Three Consecutive Odds](https://leetcode.com/problems/three-consecutive-odds/) | [C++](./algorithms/cpp/threeConsecutiveOdds/ThreeConsecutiveOdds.cpp)|Easy|
 |1541|[Minimum Insertions to Balance a Parentheses String](https://leetcode.com/problems/minimum-insertions-to-balance-a-parentheses-string/) | [C++](./algorithms/cpp/minimumInsertionsToBalanceAParenthesesString/MinimumInsertionsToBalanceAParenthesesString.cpp)|Medium|
 |1535|[Find the Winner of an Array Game](https://leetcode.com/problems/find-the-winner-of-an-array-game/) | [C++](./algorithms/cpp/findTheWinnerOfAnArrayGame/FindTheWinnerOfAnArrayGame.cpp)|Medium|
+|1513|[Number of Substrings With Only 1s](https://leetcode.com/problems/number-of-substrings-with-only-1s/) | [C++](./algorithms/cpp/numberOfSubstringsWithOnly1s/NumberOfSubstringsWithOnly1s.cpp)|Medium|
 |1470|[Shuffle the Array](https://leetcode.com/problems/shuffle-the-array/) | [C++](./algorithms/cpp/shuffleTheArray/ShuffleTheArray.cpp)|Easy|
 |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|

algorithms/cpp/numberOfSubstringsWithOnly1s/NumberOfSubstringsWithOnly1s.cpp

@@ -0,0 +1,70 @@
+// Source : https://leetcode.com/problems/number-of-substrings-with-only-1s/
+// Author : Hao Chen
+// Date   : 2020-10-03
+
+/***************************************************************************************************** 
+ *
+ * Given a binary string s (a string consisting only of '0' and '1's).
+ * 
+ * Return the number of substrings with all characters 1's.
+ * 
+ * Since the answer may be too large, return it modulo 10^9 + 7.
+ * 
+ * Example 1:
+ * 
+ * Input: s = "0110111"
+ * Output: 9
+ * Explanation: There are 9 substring in total with only 1's characters.
+ * "1" -> 5 times.
+ * "11" -> 3 times.
+ * "111" -> 1 time.
+ * 
+ * Example 2:
+ * 
+ * Input: s = "101"
+ * Output: 2
+ * Explanation: Substring "1" is shown 2 times in s.
+ * 
+ * Example 3:
+ * 
+ * Input: s = "111111"
+ * Output: 21
+ * Explanation: Each substring contains only 1's characters.
+ * 
+ * Example 4:
+ * 
+ * Input: s = "000"
+ * Output: 0
+ * 
+ * Constraints:
+ * 
+ * 	s[i] == '0' or s[i] == '1'
+ * 	1 <= s.length <= 10^5
+ ******************************************************************************************************/
+
+class Solution {
+public:
+    // 11 - 1+2
+    // 111 - 1+2+3
+    // 1111 - 1+2+3+4
+    // 11111 - 1+2+3+4+5
+    // so, we just simply find the length of continuous '1',
+    // then, the answer it len*(len+1)/2
+    int numSub(string s) {
+       long long len=0;
+       long long result=0;
+        for (auto c : s) {
+            if (c=='1') {
+                len++;
+                continue;
+            }
+            if (len > 0){
+                result += len*(len+1)/2;
+                len = 0;
+            }
+        }
+
+        result += len*(len+1)/2;
+        return result % 1000000007 ;
+    }
+};

algorithms/cpp/thousandSeparator/ThousandSeparator.cpp

@@ -0,0 +1,52 @@
+// Source : https://leetcode.com/problems/thousand-separator/
+// Author : Hao Chen
+// Date   : 2020-10-03
+
+/***************************************************************************************************** 
+ *
+ * Given an integer n, add a dot (".") as the thousands separator and return it in string format.
+ * 
+ * Example 1:
+ * 
+ * Input: n = 987
+ * Output: "987"
+ * 
+ * Example 2:
+ * 
+ * Input: n = 1234
+ * Output: "1.234"
+ * 
+ * Example 3:
+ * 
+ * Input: n = 123456789
+ * Output: "123.456.789"
+ * 
+ * Example 4:
+ * 
+ * Input: n = 0
+ * Output: "0"
+ * 
+ * Constraints:
+ * 
+ * 	0 <= n < 2^31
+ ******************************************************************************************************/
+
+class Solution {
+public:
+    string thousandSeparator(int n) {
+        if (n==0) return "0";
+        int cnt=0;
+        string result;
+        while( n > 0 ){
+            int m = n % 10;
+            result.insert(result.begin(),   ('0' + m) );
+            cnt++;
+            n /= 10;
+            if (cnt % 3 == 0 && n > 0) {
+                result = '.' + result;
+            }
+
+        }
+        return result;
+    }
+};