New Problem Solution "1524. Number of Sub-arrays With Odd Sum"

README.md

@@ -17,6 +17,7 @@ LeetCode
 |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|
 |1525|[Number of Good Ways to Split a String](https://leetcode.com/problems/number-of-good-ways-to-split-a-string/) | [C++](./algorithms/cpp/numberOfGoodWaysToSplitAString/NumberOfGoodWaysToSplitAString.cpp)|Medium|
+|1524|[Number of Sub-arrays With Odd Sum](https://leetcode.com/problems/number-of-sub-arrays-with-odd-sum/) | [C++](./algorithms/cpp/numberOfSubArraysWithOddSum/NumberOfSubArraysWithOddSum.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|

algorithms/cpp/numberOfSubArraysWithOddSum/NumberOfSubArraysWithOddSum.cpp

@@ -0,0 +1,71 @@
+// Source : https://leetcode.com/problems/number-of-sub-arrays-with-odd-sum/
+// Author : Hao Chen
+// Date   : 2020-10-07
+
+/***************************************************************************************************** 
+ *
+ * Given an array of integers arr. Return the number of sub-arrays with odd sum.
+ * 
+ * As the answer may grow large, the answer must be computed modulo 10^9 + 7.
+ * 
+ * Example 1:
+ * 
+ * Input: arr = [1,3,5]
+ * Output: 4
+ * Explanation: All sub-arrays are [[1],[1,3],[1,3,5],[3],[3,5],[5]]
+ * All sub-arrays sum are [1,4,9,3,8,5].
+ * Odd sums are [1,9,3,5] so the answer is 4.
+ * 
+ * Example 2:
+ * 
+ * Input: arr = [2,4,6]
+ * Output: 0
+ * Explanation: All sub-arrays are [[2],[2,4],[2,4,6],[4],[4,6],[6]]
+ * All sub-arrays sum are [2,6,12,4,10,6].
+ * All sub-arrays have even sum and the answer is 0.
+ * 
+ * Example 3:
+ * 
+ * Input: arr = [1,2,3,4,5,6,7]
+ * Output: 16
+ * 
+ * Example 4:
+ * 
+ * Input: arr = [100,100,99,99]
+ * Output: 4
+ * 
+ * Example 5:
+ * 
+ * Input: arr = [7]
+ * Output: 1
+ * 
+ * Constraints:
+ * 
+ * 	1 <= arr.length <= 10^5
+ * 	1 <= arr[i] <= 100
+ ******************************************************************************************************/
+
+class Solution {
+public:
+    int numOfSubarrays(vector<int>& arr) {
+        //Walk through the array, and calculate the current sum
+        //if current sum is odd, then all of the sum are evil previously are valid sub-array
+        //if current sum is evil, then all of the sum are odd previously are valid sub-array
+        int odd_sum_cnt=0, evil_sum_cnt=0;
+        int sum = 0;
+        long long result=0;
+        for (auto a : arr) {
+            sum += a;
+            if (sum % 2 == 0) {
+                evil_sum_cnt++;
+                result += odd_sum_cnt;
+            }else {
+                odd_sum_cnt++;
+                result += evil_sum_cnt + 1;
+            }
+        }
+
+        return result % 1000000007;
+
+    }
+};