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feat(Swift): update min_cost_climbing_stairs_dp and hash_map_open_addressing (#792)

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This commit is contained in:
nuomi1
2023-09-24 09:50:09 -05:00
committed by GitHub
parent ff8e7ceec5
commit 72f243eec3
3 changed files with 80 additions and 52 deletions
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codes/swift/chapter_computational_complexity/recursion.swift
+22
View File
@@ -16,6 +16,25 @@ func recur(n: Int) -> Int {
return n + res
}
/* 使用迭代模拟递归 */
func forLoopRecur(n: Int) -> Int {
// 使用一个显式的栈来模拟系统调用栈
var stack: [Int] = []
var res = 0
// 递：递归调用
for i in stride(from: n, to: 0, by: -1) {
// 通过“入栈操作”模拟“递”
stack.append(i)
}
// 归：返回结果
while !stack.isEmpty {
// 通过“出栈操作”模拟“归”
res += stack.removeLast()
}
// res = 1+2+3+...+n
return res
}
/* 尾递归 */
func tailRecur(n: Int, res: Int) -> Int {
// 终止条件
@@ -48,6 +67,9 @@ enum Recursion {
res = recursion.recur(n: n)
print("\n递归函数的求和结果 res = \(res)")
res = recursion.forLoopRecur(n: n)
print("\n使用迭代模拟递归求和结果 res = \(res)")
res = recursion.tailRecur(n: n, res: 0)
print("\n尾递归函数的求和结果 res = \(res)")
codes/swift/chapter_dynamic_programming/min_cost_climbing_stairs_dp.swift
+2 -2
View File
@@ -13,8 +13,8 @@ func minCostClimbingStairsDP(cost: [Int]) -> Int {
// 初始化 dp 表，用于存储子问题的解
var dp = Array(repeating: 0, count: n + 1)
// 初始状态：预设最小子问题的解
dp[1] = 1
dp[2] = 2
dp[1] = cost[1]
dp[2] = cost[2]
// 状态转移：从较小子问题逐步求解较大子问题
for i in stride(from: 3, through: n, by: 1) {
dp[i] = min(dp[i - 1], dp[i - 2]) + cost[i]
codes/swift/chapter_hashing/hash_map_open_addressing.swift
+56 -50
View File
@@ -13,7 +13,7 @@ class HashMapOpenAddressing {
var loadThres: Double // 触发扩容的负载因子阈值
var extendRatio: Int // 扩容倍数
var buckets: [Pair?] // 桶数组
var removed: Pair // 删除标记
var TOMBSTONE: Pair // 删除标记
/* 构造方法 */
init() {
@@ -22,7 +22,7 @@ class HashMapOpenAddressing {
loadThres = 2.0 / 3.0
extendRatio = 2
buckets = Array(repeating: nil, count: capacity)
removed = Pair(key: -1, val: "-1")
TOMBSTONE = Pair(key: -1, val: "-1")
}
/* 哈希函数 */
@@ -35,22 +35,42 @@ class HashMapOpenAddressing {
Double(size / capacity)
}
/* 搜索 key 对应的桶索引 */
func findBucket(key: Int) -> Int {
var index = hashFunc(key: key)
var firstTombstone = -1
// 线性探测，当遇到空桶时跳出
while buckets[index] != nil {
// 若遇到 key ，返回对应桶索引
if buckets[index]!.key == key {
// 若之前遇到了删除标记，则将键值对移动至该索引
if firstTombstone != -1 {
buckets[firstTombstone] = buckets[index]
buckets[index] = TOMBSTONE
return firstTombstone // 返回移动后的桶索引
}
return index // 返回桶索引
}
// 记录遇到的首个删除标记
if firstTombstone == -1 && buckets[index] == TOMBSTONE {
firstTombstone = index
}
// 计算桶索引，越过尾部返回头部
index = (index + 1) % capacity
}
// 若 key 不存在，则返回添加点的索引
return firstTombstone == -1 ? index : firstTombstone
}
/* 查询操作 */
func get(key: Int) -> String? {
let index = hashFunc(key: key)
// 线性探测，从 index 开始向后遍历
for i in stride(from: 0, to: capacity, by: 1) {
// 计算桶索引，越过尾部返回头部
let j = (index + i) % capacity
// 若遇到空桶，说明无此 key ，则返回 nil
if buckets[j] == nil {
return nil
}
// 若遇到指定 key ，则返回对应 val
if buckets[j]?.key == key, buckets[j] != removed {
return buckets[j]?.val
}
// 搜索 key 对应的桶索引
let index = findBucket(key: key)
// 若找到键值对，则返回对应 val
if buckets[index] != nil, buckets[index] != TOMBSTONE {
return buckets[index]!.val
}
// 若键值对不存在，则返回 null
return nil
}
@@ -60,42 +80,26 @@ class HashMapOpenAddressing {
if loadFactor() > loadThres {
extend()
}
let index = hashFunc(key: key)
// 线性探测，从 index 开始向后遍历
for i in stride(from: 0, through: capacity, by: 1) {
// 计算桶索引，越过尾部返回头部
let j = (index + i) % capacity
// 若遇到空桶、或带有删除标记的桶，则将键值对放入该桶
if buckets[j] == nil || buckets[j] == removed {
buckets[j] = Pair(key: key, val: val)
size += 1
return
}
// 若遇到指定 key ，则更新对应 val
if buckets[j]?.key == key {
buckets[j]?.val = val
return
}
// 搜索 key 对应的桶索引
let index = findBucket(key: key)
// 若找到键值对，则覆盖 val 并返回
if buckets[index] != nil, buckets[index] != TOMBSTONE {
buckets[index]!.val = val
return
}
// 若键值对不存在，则添加该键值对
buckets[index] = Pair(key: key, val: val)
size += 1
}
/* 删除操作 */
func remove(key: Int) {
let index = hashFunc(key: key)
// 线性探测，从 index 开始向后遍历
for i in stride(from: 0, to: capacity, by: 1) {
// 计算桶索引，越过尾部返回头部
let j = (index + i) % capacity
// 若遇到空桶，说明无此 key ，则直接返回
if buckets[j] == nil {
return
}
// 若遇到指定 key ，则标记删除并返回
if buckets[j]?.key == key {
buckets[j] = removed
size -= 1
return
}
// 搜索 key 对应的桶索引
let index = findBucket(key: key)
// 若找到键值对，则用删除标记覆盖它
if buckets[index] != nil, buckets[index] != TOMBSTONE {
buckets[index] = TOMBSTONE
size -= 1
}
}
@@ -109,7 +113,7 @@ class HashMapOpenAddressing {
size = 0
// 将键值对从原哈希表搬运至新哈希表
for pair in bucketsTmp {
if let pair, pair != removed {
if let pair, pair != TOMBSTONE {
put(key: pair.key, val: pair.val)
}
}
@@ -118,10 +122,12 @@ class HashMapOpenAddressing {
/* 打印哈希表 */
func print() {
for pair in buckets {
if let pair {
Swift.print("\(pair.key) -> \(pair.val)")
} else {
if pair == nil {
Swift.print("null")
} else if pair == TOMBSTONE {
Swift.print("TOMBSTONE")
} else {
Swift.print("\(pair!.key) -> \(pair!.val)")
}
}
}