Create divide-array-into-equal-pairs.cpp

Author: kamyu104

C++/divide-array-into-equal-pairs.cpp

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+// Time:  O(n)
+// Space: O(n)
+
+// freq table
+class Solution {
+public:
+    bool divideArray(vector<int>& nums) {
+        unordered_map<int, int> odd;
+        for (const auto& x : nums) {
+            odd[x] = (odd[x] + 1) % 2;
+        }
+        return all_of(cbegin(odd), cend(odd), [](const auto& x) {
+            return x.second == 0;
+        });
+    }
+};