The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,
F(0) = 0, F(1) = 1 F(n) = F(n - 1) + F(n - 2), for n > 1.
Given n, calculate F(n).
Example 1:
Input: n = 2 Output: 1 Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
Example 2:
Input: n = 3 Output: 2 Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
Example 3:
Input: n = 4 Output: 3 Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
Constraints:
0 <= n <= 30class Solution {
public int fib(int n) {
if (n <= 1)
return n;
int n1 = 0, n2 = 1;
for (int i = 2; i <= n; i++) {
int temp = n2;
n2 += n1;
n1 = temp;
}
return n2;
}
}class Solution {
public int fib(int n) {
int[] memo = new int[n + 1];
return solve(n, memo);
}
private int solve(int n, int[] memo) {
if (n <= 1)
return n;
if (memo[n] != 0)
return memo[n];
return memo[n] = solve(n - 2, memo) + solve(n - 1, memo);
}
}class Solution {
public int fib(int n) {
if (n <= 1)
return n;
return fib(n - 2) + fib(n - 1);
}
}class Solution {
public int fib(int n) {
if (n <= 1)
return n;
int n1 = 0, n2 = 1;
for (int i = 2; i <= n; i++) {
int temp = n2;
n2 += n1;
n1 = temp;
}
return n2;
}
}