Create number-of-longest-increasing-subsequence.cpp

Author: kamyu104

C++/number-of-longest-increasing-subsequence.cpp

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+// Time:  O(n^2)
+// Space: O(n)
+
+class Solution {
+public:
+    int findNumberOfLIS(vector<int>& nums) {
+        auto result = 0, max_len = 0;
+        vector<pair<int, int>> dp(nums.size(), {1, 1});  // {length, number} pair
+        for (int i = 0; i < nums.size(); ++i) {
+            for (int j = 0; j < i; ++j) {
+                if (nums[i] > nums[j]) {
+                    if (dp[i].first == dp[j].first + 1) {
+                        dp[i].second += dp[j].second;
+                    } else if (dp[i].first < dp[j].first + 1) {
+                        dp[i] = {dp[j].first + 1, dp[j].second};
+                    }
+                }
+            }
+            if (max_len == dp[i].first) {
+                result += dp[i].second;
+            } else if (max_len < dp[i].first) {
+                max_len = dp[i].first;
+                result = dp[i].second;
+            }
+        }
+        return result;
+    }
+};