动态规划
class Solution {
public int climbStairs(int n) {
if(n <= 2) return n;
int[] dp = new int[n + 1];
dp[1] = 1;
dp[2] = 2;
for(int i = 3; i <= n; i++){
dp[i] = dp[i - 1] + dp[i - 2];
}
return dp[n];
}
}
压缩空间
class Solution {
public int climbStairs(int n) {
if(n <= 2) return n;
int a = 1;
int b = 2;
for(int i = 3; i <= n; i++){
int c = a + b;
a = b;
b = c;
}
return b;
}
}