Nth Fibonacci (iterative)
Medium
Java
Control Flow
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Problem Statement
Task: return nth Fibonacci number (0-indexed) using iterative loop.
Input Format
An integer n (0-indexed position).
Output Format
The nth Fibonacci number.
Example
7
13
Constraints
• n ≥ 0
• Use iterative loop only (no recursion)
• Use iterative loop only (no recursion)
Concept Explanation
Fibonacci sequence (0-indexed):
0, 1, 1, 2, 3, 5, 8, 13, ...
Each number is the sum of the previous two.
0, 1, 1, 2, 3, 5, 8, 13, ...
Each number is the sum of the previous two.
Step-by-Step Explanation
1.Read integer n.
2.If n == 0, return 0.
3.If n == 1, return 1.
4.Initialize:
• a = 0 (F(0))
• b = 1 (F(1))
5.Loop from 2 to n:
• c = a + b
• a = b
• b = c
6.After loop ends, return b.
2.If n == 0, return 0.
3.If n == 1, return 1.
4.Initialize:
• a = 0 (F(0))
• b = 1 (F(1))
5.Loop from 2 to n:
• c = a + b
• a = b
• b = c
6.After loop ends, return b.
Concept Explanation
Fibonacci sequence (0-indexed):
0, 1, 1, 2, 3, 5, 8, 13, ...
Each number is the sum of the previous two.
0, 1, 1, 2, 3, 5, 8, 13, ...
Each number is the sum of the previous two.
Step-by-Step Explanation
1.Read integer n.
2.If n == 0, return 0.
3.If n == 1, return 1.
4.Initialize:
• a = 0 (F(0))
• b = 1 (F(1))
5.Loop from 2 to n:
• c = a + b
• a = b
• b = c
6.After loop ends, return b.
2.If n == 0, return 0.
3.If n == 1, return 1.
4.Initialize:
• a = 0 (F(0))
• b = 1 (F(1))
5.Loop from 2 to n:
• c = a + b
• a = b
• b = c
6.After loop ends, return b.
Input / Output Format
Input Format
An integer n (0-indexed position).
Output Format
The nth Fibonacci number.
Constraints
• n ≥ 0
• Use iterative loop only (no recursion)
• Use iterative loop only (no recursion)
Examples
Input:
7
Output:
13
Example Solution (Public)
static long fib(int n){long a=0,b=1;for(int i=0;i<n;i++){long t=a+b;a=b;b=t;}return a;}
Official Solution Code
static long fib(int n){long a=0,b=1;for(int i=0;i<n;i++){long t=a+b;a=b;b=t;}return a;}
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