From 606284a2f4921126373584e5fd3fb24ee7b42add Mon Sep 17 00:00:00 2001
From: chayan das <110921638+Chayandas07@users.noreply.github.com>
Date: Thu, 27 Feb 2025 20:42:32 +0530
Subject: [PATCH] Create 873. Length of Longest Fibonacci Subsequence

---
 873. Length of Longest Fibonacci Subsequence | 26 ++++++++++++++++++++
 1 file changed, 26 insertions(+)
 create mode 100644 873. Length of Longest Fibonacci Subsequence

diff --git a/873. Length of Longest Fibonacci Subsequence b/873. Length of Longest Fibonacci Subsequence
new file mode 100644
index 0000000..3b3e422
--- /dev/null
+++ b/873. Length of Longest Fibonacci Subsequence	
@@ -0,0 +1,26 @@
+class Solution {
+public:
+    int lenLongestFibSubseq(vector<int>& arr) {
+        int  n = arr.size();
+        unordered_map<int,int>mp; // element->index
+        for(int i=0; i<n; i++){
+            mp[arr[i]] = i;
+        }
+        vector<vector<int>>dp(n,vector<int>(n,2));
+        int maxLen = 0;
+        
+        for(int i=0; i<n-1;i++){
+            for(int j=i+1; j<n;j++){
+                int next = arr[i] + arr[j];
+                if(mp.find(next) != mp.end()){
+                    int k = mp[next];
+                    if(k>j){
+                        dp[j][k] = 1 + dp[i][j];
+                        maxLen = max(maxLen,dp[j][k]);
+                    }
+                }
+            }
+        }  
+        return maxLen > 2 ? maxLen : 0;
+    }
+};