41 lines
974 B
Swift
41 lines
974 B
Swift
/**
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* File: climbing_stairs_dfs_mem.swift
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* Created Time: 2023-07-15
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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/* 记忆化搜索 */
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func dfs(i: Int, mem: inout [Int]) -> Int {
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// 已知 dp[1] 和 dp[2] ，返回之
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if i == 1 || i == 2 {
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return i
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}
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// 若存在记录 dp[i] ，则直接返回之
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if mem[i] != -1 {
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return mem[i]
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}
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// dp[i] = dp[i-1] + dp[i-2]
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let count = dfs(i: i - 1, mem: &mem) + dfs(i: i - 2, mem: &mem)
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// 记录 dp[i]
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mem[i] = count
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return count
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}
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/* 爬楼梯：记忆化搜索 */
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func climbingStairsDFSMem(n: Int) -> Int {
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// mem[i] 记录爬到第 i 阶的方案总数，-1 代表无记录
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var mem = Array(repeating: -1, count: n + 1)
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return dfs(i: n, mem: &mem)
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}
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@main
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enum ClimbingStairsDFSMem {
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/* Driver Code */
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static func main() {
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let n = 9
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let res = climbingStairsDFSMem(n: n)
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print("爬 \(n) 阶楼梯共有 \(res) 种方案")
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}
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}
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