I wanted to compute 80th term of the
Fibonacci series. I wrote the rampant recursive function,
int fib(int n){
return (1==n || 2==n) ? 1 :
fib(n-1) + fib(n-2);
}
and waited for the result. I wait… and wait…
and wait…
With an 8GB RAM and an Intel i5 CPU, why is
it taking so long? I terminated the process and tried computing the 40th
term. It took about a second. I put a check and was shocked to find that the above
recursive function was called 204,668,309 times while computing the 40th
term.
More than 200 million times? Is it reporting
function calls or scam of some government?
The Dynamic Programming solution computes 100th
Fibonacci term in less than fraction of a second, with a single function call, taking
linear time and constant extra memory.
A recursive solution, usually, neither pass all
test cases in a coding competition, nor does it impress the interviewer in an
interview of company like Google, Microsoft, etc.
The most difficult questions asked in competitions
and interviews, are from dynamic programming. This book takes Dynamic
Programming head-on. It first explain the concepts with simple examples and
then deep dives into complex DP problems.
I wanted to compute 80th term of the
Fibonacci series. I wrote the rampant recursive function,
int fib(int n){
return (1==n || 2==n) ? 1 :
fib(n-1) + fib(n-2);
}
and waited for the result. I wait… and wait…
and wait…
With an 8GB RAM and an Intel i5 CPU, why is
it taking so long? I terminated the process and tried computing the 40th
term. It took about a second. I put a check and was shocked to find that the above
recursive function was called 204,668,309 times while computing the 40th
term.
More than 200 million times? Is it reporting
function calls or scam of some government?
The Dynamic Programming solution computes 100th
Fibonacci term in less than fraction of a second, with a single function call, taking
linear time and constant extra memory.
A recursive solution, usually, neither pass all
test cases in a coding competition, nor does it impress the interviewer in an
interview of company like Google, Microsoft, etc.
The most difficult questions asked in competitions
and interviews, are from dynamic programming. This book takes Dynamic
Programming head-on. It first explain the concepts with simple examples and
then deep dives into complex DP problems.
