feat(csharp): add forLoopRecur and new HashMapOpenAddressing (#783)
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hpstory
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@ -18,6 +18,25 @@ public class recursion {
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return n + res;
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}
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/* 使用迭代模拟递归 */
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public int forLoopRecur(int n) {
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// 使用一个显式的栈来模拟系统调用栈
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Stack<int> stack = new Stack<int>();
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int res = 0;
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// 递：递归调用
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for (int i = n; i > 0; i--) {
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// 通过“入栈操作”模拟“递”
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stack.Push(i);
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}
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// 归：返回结果
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while (stack.Count > 0) {
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// 通过“出栈操作”模拟“归”
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res += stack.Pop();
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}
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// res = 1+2+3+...+n
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return res;
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}
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/* 尾递归 */
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public int tailRecur(int n, int res) {
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// 终止条件
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@ -47,6 +66,9 @@ public class recursion {
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res = recur(n);
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Console.WriteLine("\n递归函数的求和结果 res = " + res);
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res = forLoopRecur(n);
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Console.WriteLine("\n使用迭代模拟递归求和结果 res = " + res);
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res = tailRecur(n, 0);
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Console.WriteLine("\n尾递归函数的求和结果 res = " + res);
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@ -8,21 +8,17 @@ namespace hello_algo.chapter_hashing;
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/* 开放寻址哈希表 */
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class HashMapOpenAddressing {
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int size; // 键值对数量
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int capacity; // 哈希表容量
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double loadThres; // 触发扩容的负载因子阈值
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int extendRatio; // 扩容倍数
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Pair[] buckets; // 桶数组
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Pair removed; // 删除标记
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private int size; // 键值对数量
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private int capacity = 4; // 哈希表容量
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private double loadThres = 2.0 / 3; // 触发扩容的负载因子阈值
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private int extendRatio = 2; // 扩容倍数
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private Pair[] buckets; // 桶数组
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private Pair TOMBSTONE = new Pair(-1, "-1"); // 删除标记
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/* 构造方法 */
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public HashMapOpenAddressing() {
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size = 0;
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capacity = 4;
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loadThres = 2.0 / 3.0;
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extendRatio = 2;
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buckets = new Pair[capacity];
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removed = new Pair(-1, "-1");
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}
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/* 哈希函数 */
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@ -35,20 +31,42 @@ class HashMapOpenAddressing {
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return (double)size / capacity;
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}
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/* 搜索 key 对应的桶索引 */
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private int findBucket(int key) {
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int index = hashFunc(key);
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int firstTombstone = -1;
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// 线性探测，当遇到空桶时跳出
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while (buckets[index] != null) {
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// 若遇到 key ，返回对应桶索引
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if (buckets[index].key == key) {
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// 若之前遇到了删除标记，则将键值对移动至该索引
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if (firstTombstone != -1) {
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buckets[firstTombstone] = buckets[index];
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buckets[index] = TOMBSTONE;
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return firstTombstone; // 返回移动后的桶索引
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}
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return index; // 返回桶索引
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}
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// 记录遇到的首个删除标记
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if (firstTombstone == -1 && buckets[index] == TOMBSTONE) {
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firstTombstone = index;
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}
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// 计算桶索引，越过尾部返回头部
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index = (index + 1) % capacity;
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}
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// 若 key 不存在，则返回添加点的索引
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return firstTombstone == -1 ? index : firstTombstone;
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}
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/* 查询操作 */
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public string get(int key) {
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int index = hashFunc(key);
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// 线性探测，从 index 开始向后遍历
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for (int i = 0; i < capacity; i++) {
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// 计算桶索引，越过尾部返回头部
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int j = (index + i) % capacity;
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// 若遇到空桶，说明无此 key ，则返回 null
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if (buckets[j] == null)
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return null;
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// 若遇到指定 key ，则返回对应 val
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if (buckets[j].key == key && buckets[j] != removed)
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return buckets[j].val;
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// 搜索 key 对应的桶索引
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int index = findBucket(key);
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// 若找到键值对，则返回对应 val
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if (buckets[index] != null && buckets[index] != TOMBSTONE) {
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return buckets[index].val;
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}
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// 若键值对不存在，则返回 null
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return null;
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}
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@ -58,42 +76,26 @@ class HashMapOpenAddressing {
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if (loadFactor() > loadThres) {
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extend();
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}
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int index = hashFunc(key);
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// 线性探测，从 index 开始向后遍历
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for (int i = 0; i < capacity; i++) {
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// 计算桶索引，越过尾部返回头部
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int j = (index + i) % capacity;
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// 若遇到空桶、或带有删除标记的桶，则将键值对放入该桶
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if (buckets[j] == null || buckets[j] == removed) {
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buckets[j] = new Pair(key, val);
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size += 1;
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return;
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}
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// 若遇到指定 key ，则更新对应 val
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if (buckets[j].key == key) {
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buckets[j].val = val;
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return;
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}
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// 搜索 key 对应的桶索引
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int index = findBucket(key);
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// 若找到键值对，则覆盖 val 并返回
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if (buckets[index] != null && buckets[index] != TOMBSTONE) {
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buckets[index].val = val;
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return;
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}
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// 若键值对不存在，则添加该键值对
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buckets[index] = new Pair(key, val);
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size++;
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}
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/* 删除操作 */
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public void remove(int key) {
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int index = hashFunc(key);
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// 线性探测，从 index 开始向后遍历
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for (int i = 0; i < capacity; i++) {
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// 计算桶索引，越过尾部返回头部
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int j = (index + i) % capacity;
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// 若遇到空桶，说明无此 key ，则直接返回
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if (buckets[j] == null) {
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return;
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}
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// 若遇到指定 key ，则标记删除并返回
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if (buckets[j].key == key) {
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buckets[j] = removed;
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size -= 1;
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return;
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}
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// 搜索 key 对应的桶索引
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int index = findBucket(key);
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// 若找到键值对，则用删除标记覆盖它
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if (buckets[index] != null && buckets[index] != TOMBSTONE) {
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buckets[index] = TOMBSTONE;
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size--;
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}
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}
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@ -107,7 +109,7 @@ class HashMapOpenAddressing {
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size = 0;
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// 将键值对从原哈希表搬运至新哈希表
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foreach (Pair pair in bucketsTmp) {
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if (pair != null && pair != removed) {
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if (pair != null && pair != TOMBSTONE) {
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put(pair.key, pair.val);
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}
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}
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@ -116,10 +118,12 @@ class HashMapOpenAddressing {
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/* 打印哈希表 */
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public void print() {
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foreach (Pair pair in buckets) {
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if (pair != null) {
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Console.WriteLine(pair.key + " -> " + pair.val);
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} else {
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if (pair == null) {
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Console.WriteLine("null");
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} else if (pair == TOMBSTONE) {
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Console.WriteLine("TOMBSTONE");
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} else {
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Console.WriteLine(pair.key + " -> " + pair.val);
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}
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}
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}
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