446. Arithmetic Slices II - Subsequence

Author: gzc

cpp/441-450/Arithmetic Slices II - Subsequence.cpp

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+class Solution {
+public:
+    int numberOfArithmeticSlices(vector<int>& A) {
+        int n = A.size();
+        vector<map<int, int>> dp(n);
+        int ans = 0;
+        
+        for (int i = 0; i < n; i++) {
+            // dp[x][delta] += dp[y][delta] + 1（y∈[0, x - 1]）
+            for (int j = 0; j < i; j++) {
+                long delta = (long)A[i] - (long)A[j];
+                if (delta > INT_MAX || delta < INT_MIN) continue;
+                dp[i][delta]++;
+                if (dp[j].find(delta) != dp[j].end()) {
+                    dp[i][delta] += dp[j][delta];
+                    ans += dp[j][delta];
+                }
+            }
+            
+        }
+        
+        return ans;
+    }
+};