Create ways-to-split-array-into-three-subarrays.cpp

Author: kamyu104

C++/ways-to-split-array-into-three-subarrays.cpp

@@ -0,0 +1,28 @@
+// Time:  O(n)
+// Space: O(n)
+
+class Solution {
+public:
+    int waysToSplit(vector<int>& nums) {
+        static const int MOD = 1e9 + 7;
+        
+        vector<int> prefix(1);
+        for (const auto& x : nums) {
+            prefix.emplace_back(prefix.back() + x);
+        }
+
+        int result = 0, left = 0, right = 0;
+        for (int i = 0; i < size(nums); ++i) {
+            left = max(left, i + 1);
+            while (left + 1 < size(nums) && prefix[i + 1] > prefix[left + 1] - prefix[i + 1]) {
+                ++left;
+            }
+            right = max(right, left);
+            while (right + 1 < size(nums) && prefix[right + 1] - prefix[i + 1] <= prefix.back() - prefix[right + 1]) {
+                ++right;
+            }
+            result = (result + (right - left)) % MOD;
+        }
+        return result;
+    }
+};