ClimbStairs
ClimbStairs.java 源码
package datastructure.array.leetcode;
import java.util.HashMap;
import java.util.Map;
/**
* @author roseduan
* @time 2020/9/7 9:41 下午
* @description 爬楼梯
*/
public class ClimbStairs {
private static final Map<Integer, Integer> mem = new HashMap<>();
/**
* 递归
*/
public int climbStairs1(int n){
if (n <= 2){
return n;
}
return climbStairs1(n - 1) + climbStairs1(n - 2);
}
/**
* 备忘录
*/
public int climbStairs2(int n){
if (n <= 2) {
return n;
}
if (mem.containsKey(n)){
return mem.get(n);
}
int res = climbStairs2(n - 1) + climbStairs2(n - 2);
mem.put(n, res);
return res;
}
/**
* 动态规划
*/
public int climbStairs3(int n){
if (n <= 2){
return n;
}
int prev = 1, next = 2;
for (int i = 2; i < n; i++) {
int temp = prev + next;
prev = next;
next = temp;
}
return next;
}
}
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