Update 02 - Top-Down | DP | Approach.cpp

Author: JawadSher

24 - Dynamic Programming Problems/01 - Example | Nth Fibonacci Number/02 - Top-Down | DP | Approach.cpp

@@ -1,13 +1,23 @@
 class Solution {
   public:
     int nthFibonacci(int n) {
-        vector<int> dp(n+1,  -1);
-        
-        if(n == 1 || n == 0) return n;
-        if(dp[n] != -1) return dp[n];
-        
-        dp[n] = nthFibonacci(n-1) + nthFibonacci(n-2);
-        
+        // Create a vector to store computed Fibonacci values, initialized to -1.
+        // This is used for memoization to avoid redundant calculations.
+        vector<int> dp(n + 1, -1);
+
+        // Base case: If n is 0 or 1, the Fibonacci value is n itself.
+        if (n == 0 || n == 1) 
+            return n;
+
+        // Check if the value for the nth Fibonacci number is already computed.
+        // If dp[n] is not -1, it means the value is already stored in the memoization table.
+        if (dp[n] != -1) 
+            return dp[n];
+
+        // Recursive case: Compute the nth Fibonacci number by summing the (n-1)th and (n-2)th numbers.
+        dp[n] = nthFibonacci(n - 1) + nthFibonacci(n - 2);
+
+        // Store the computed value in dp[n] and return it.
         return dp[n];
     }
 };