//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 yo
//u 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
//
// Related Topics Math Dynamic Programming Memoization
// 👍 13325 👎 398
//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
public int climbStairs(int n) {
if (n <= 0) {
return 0;
}
if (n == 1) {
return 1;
}
if (n == 2) {
return 2;
}
int first = 1, second = 2, third = 0;
for (int i = 3; i <= n; i++) {
third = first + second;
first = second;
second = third;
}
return third;
}
}
//leetcode submit region end(Prohibit modification and deletion)
