一、 509. 斐波那契数
题目链接：https://leetcode.cn/problems/fibonacci-number/
class Solution {
public int fib(int n) {
if (n <= 1) return n;
int[] dp = new int[n + 1];
dp[0] = 0;
dp[1] = 1;
for (int i = 2; i <= n; i++) {
dp[i] = dp[i - 1] + dp[i -2];
}
return dp[n];
}
}
class Solution {
public int fib(int n) {
if (n <= 1) return n;
int a = 0;
int b = 1;
int c = 0;
for (int i = 2; i <= n; i++) {
c = a + b;
a = b;
b = c;
}
return c;
}
}
二、 70. 爬楼梯
题目链接：https://leetcode.cn/problems/climbing-stairs/
class Solution {
public int climbStairs(int n) {
if (n <= 1) 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];
}
}
三、746. 使用最小花费爬楼梯
题目链接：https://leetcode.cn/problems/min-cost-climbing-stairs/
class Solution {
public int minCostClimbingStairs(int[] cost) {
int len = cost.length;
int[] dp = new int[len + 1];
dp[0] = 0;
dp[1] = 0;
for (int i = 2; i < len + 1; i++) {
dp[i] = Math.min(dp[i - 1] + cost[i - 1], dp[i - 2] + cost[i - 2]);
}
return dp[len];
}
}
