LeetCode-in-All
70. Climbing Stairs
Easy
You are climbing a staircase. It takes n steps to reach the top.
Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
Example 1:
Input: n = 2
Output: 2
Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps
Example 2:
Input: n = 3
Output: 3
Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step
Constraints:
1 <= n <= 45
Solution
class Solution {
/**
* @param Integer $n
* @return Integer
*/
public function climbStairs($n) {
if ($n < 2) {
return $n;
}
$cache = array_fill(0, $n, 0);
// creating a cache or DP to store the result
// so that we dont have to iterate multiple times
// for the same values;
// for 0 and 1 the result array i.e cache values would be 1 and 2
// in loop we are just getting ith values i.e 5th step values from
// i-1 and i-2 which are 4th step and 3rd step values.
$cache[0] = 1;
$cache[1] = 2;
for ($i = 2; $i < $n; $i++) {
$cache[$i] = $cache[$i - 1] + $cache[$i - 2];
}
return $cache[$n - 1];
}
}