Add C++ solution of problem #873

Author: Cuda-Chen

873/solution.cpp

@@ -0,0 +1,35 @@
+// Hash table record index,
+// then find whether the target exists in hash table.
+
+class Solution {
+public:
+    int lenLongestFibSubseq(vector<int>& A) {
+        int n = A.size();
+        unordered_map<int, int> m; // {num, idx}
+        for(int i = 0; i < n; i++)
+            m[A[i]] = i;
+        int mx = A.back();
+        int ans = 0;
+        for(int i = 0; i < n - 2; i++) {
+            for(int j = i + 1; j < n - 1; j++) {
+                int f1 = A[i];
+                int f2 = A[j];
+                int tmp = f1 + f2;
+                if(!m.count(tmp))
+                    continue;
+
+                int cnt = 3;
+                while(tmp <= mx) {
+                    f1 = f2;
+                    f2 = tmp;
+                    tmp = f1 + f2;
+                    if(!m.count(tmp))
+                        break;
+                    cnt++;
+                }
+                ans = max(ans, cnt);
+            }
+        }
+        return ans;
+    }
+};