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hello-algo/codes/ruby/chapter_dynamic_programming/climbing_stairs_dfs_mem.rb

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=begin
File: climbing_stairs_dfs_mem.rb
Created Time: 2024-05-29
Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
=end
### 记忆化搜索 ###
def dfs(i, mem)
# 已知 dp[1] 和 dp[2] ,返回之
return i if i == 1 || i == 2
# 若存在记录 dp[i] ,则直接返回之
return mem[i] if mem[i] != -1
# dp[i] = dp[i-1] + dp[i-2]
count = dfs(i - 1, mem) + dfs(i - 2, mem)
# 记录 dp[i]
mem[i] = count
end
### 爬楼梯:记忆化搜索 ###
def climbing_stairs_dfs_mem(n)
# mem[i] 记录爬到第 i 阶的方案总数,-1 代表无记录
mem = Array.new(n + 1, -1)
dfs(n, mem)
end
### Driver Code ###
if __FILE__ == $0
n = 9
res = climbing_stairs_dfs_mem(n)
puts "#{n} 阶楼梯共有 #{res} 种方案"
end