做算法課設時候看到題目要求模擬函數遞歸時候棧的入棧出棧過程。本來想著直接調用系統遞歸函數即可,可是發現系統函數棧的空間非常小大約只有3000層,很容易爆棧。于是便有了用棧去模擬遞歸函數的想法,但是上網查了下貌似相關代碼比較少,讓GPT寫的代碼又牛頭不對馬嘴,于是手搓了一下。用棧模擬遞歸的過程,對遞歸過程,棧的理解都很有幫助。
二分遞歸函數模擬
第一個函數erfen為正常的二分遞歸函數,但是系統的遞歸棧最多能遞歸到3000層左右,太少了。我們可以用棧來模擬函數遞歸的過程,這樣棧的層數可以達到我們設置的數組大小,我這里設置了二十萬。
#include <iostream>using namespace std;const int N = 2e5 + 5;struct binaryFrame {int l, r;int level;//記錄當前層數int step;//記錄步數
}stackBinary[N];/*需要模擬的二分遞歸函數
int erfen(int arr[], int l, int r, int key)
{int ans = -1;int mid = l + r >> 1;if (arr[mid] == key && l == r) return r;if (l >= r) return -1;if (arr[mid] >= key) {ans = erfen(arr, l, mid, key);}else {ans = erfen(arr, mid + 1, r, key);}return ans;
}
*/void binarySearch(int arr[], int l, int r, int key, int& index)
{int nowLevel = 1, nowStep = 0, tt = 0, L = l, R = r;tt++;stackBinary[tt] = { l,r,nowLevel,nowStep };cout << "壓棧:" << "當前執行函數紙帶范圍為:(" << L << " , " << R << " )" << " 層數為" << nowLevel << " 執行步數為" << nowStep << "\n";while (L < R){int mid = L + R >> 1;if (arr[mid] >= key){R = mid;stackBinary[++tt] = { L,R,++nowLevel,++nowStep };cout << "壓棧:" << "當前執行函數紙帶范圍為:(" << L << " , " << R << " )" << " 層數為" << nowLevel << " 執行步數為" << nowStep << "\n";}else {L = mid + 1;stackBinary[++tt] = { L,R,++nowLevel,++nowStep };cout << "壓棧:" << "當前執行函數紙帶范圍為:(" << L << " , " << R << " )" << " 層數為" << nowLevel << " 執行步數為" << nowStep << "\n";}}if (arr[R] == key) {index = R;}while (tt > 0){cout << "出棧:" << "當前執行函數紙帶范圍為:(" << stackBinary[tt].l << " , " << stackBinary[tt].r << " )" << " 層數為" << stackBinary[tt].level << " 執行步數為" << stackBinary[tt].step << "\n";tt--;}}int main()
{int arr[] = { 1,2,3,4,5,6,7,8,9,10 };int n = 10;int key = 2;int index = -1;binarySearch(arr, 0, n - 1, key, index);if (index == -1) {cout << "找不到這個吊數\n";}else {cout << "這個B數在數組中的第" << index + 1 << "個位置" << "\n";}return 0;
}
顯示壓棧出棧過程
棧模擬回溯法解決01背包
#include<iostream>
#include<vector>using namespace std;typedef long long LL;const int N = 2e5 + 5;/*
// 全局變量用于存儲最終結果
int max_value = 0;
vector<int> best_set;/*
// 需要模擬的遞歸回溯函數
void knapsack(int index, int current_weight, int current_value, int capacity, const vector<int>& weights, const vector<int>& values, vector<int>& chosen_items) {// 基礎情況:如果考慮完所有物品if (index == weights.size()) {// 檢查當前物品集合是否是一個有效解if (current_weight <= capacity && current_value > max_value) {max_value = current_value;best_set = chosen_items;}return;}// 選擇當前物品chosen_items.push_back(index);knapsack(index + 1, current_weight + weights[index], current_value + values[index], capacity, weights, values, chosen_items);chosen_items.pop_back(); // 回溯// 不選擇當前物品knapsack(index + 1, current_weight, current_value, capacity, weights, values, chosen_items);
}*/struct backFrame
{int index;int current_weight;int current_value;int step;vector<int> chosenItems;int stage;
}stackBack[N];void backBag(int n, int capacity, int& max_value, vector<int>& weights, vector<int>& values, vector<int>& chosenItems, vector<int>& best_set)
{int tt = 0, nowStep = 0;stackBack[++tt] = { 0,0,0,0,{},0 };cout << "壓棧:初始化壓棧,壓入 0 0 0 0 {} 0" << "\n";while (tt > 0){backFrame now = stackBack[tt];cout << "當前執行函數層為:" << now.index << " " << now.current_weight << " " << now.current_value << " " << now.step << "\n";if (stackBack[tt].index >= n) {if (stackBack[tt].current_value > max_value && stackBack[tt].current_weight <= capacity){max_value = stackBack[tt].current_value;best_set = stackBack[tt].chosenItems;cout << "更新best_set ";for (auto i : best_set) cout << i + 1 << " ";cout << "\n";}tt--;cout << "出棧1:" << now.index << " " << now.current_weight<< " " << now.current_value << " " << now.step << "\n";continue;}if (now.stage == 0) {//棧頂為初始狀態的話直接下一層函數壓棧chosenItems.push_back(now.index);stackBack[++tt] = { now.index + 1,now.current_weight + weights[now.index],now.current_value + values[now.index],now.step + 1,chosenItems,0 };cout << "壓棧1: " << now.index + 1 << " " << now.current_weight + weights[now.index] << " " << now.current_value + values[now.index] << " " << now.step + 1 << "\n";stackBack[tt - 1].stage ++;}else if (now.stage == 1) {chosenItems.pop_back();stackBack[++tt] = { now.index + 1,now.current_weight,now.current_value,now.step + 1,chosenItems,0 };cout << "壓棧2: " << now.index + 1 << " " << now.current_weight << " " << now.current_value << " " << now.step + 1 << "\n";stackBack[tt - 1].stage ++;}else if (now.stage == 2) {tt--;cout << "出棧2:" << now.index << " " << now.current_weight<< " " << now.current_value << " " << now.step << "\n";}}}int main()
{vector<int> weights = { 1,2,3,5,7,6 };vector<int> values = { 6,5,10,30,15,25 };vector<int> chosenItems;vector<int> best_set;int capacity = 10, n = 6;int max_value = -1;/*cout << "請輸入物品件數和背包容量\n";cin >> n >> capacity;cout << "請輸入" << n << "件物品,每件物品的質量,價值\n";for (int i = 0; i < n; i++){int x, y;cin >> x >> y;weights.push_back(x);values.push_back(y);}*/backBag(n, capacity, max_value, weights, values, chosenItems, best_set);LL sum = 0;for (auto i : best_set){cout << "選擇了第" << i + 1 << "件物品\n";sum += weights[i];}cout << "可以獲得的最大價值為" << max_value << "\n";cout << "所占用的背包空間為" << sum << "\n";return 0;
}/*
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*/
棧模擬備忘錄法解決01背包
#include <iostream>
#include <vector>
#include <cstring>
#include<Windows.h>using namespace std;const int N = 2e4 + 5;int n, W;int dp[505][1005]; // 備忘錄數組
vector<int> weights;
vector<int> values;/*需要模擬的備忘錄遞歸函數
// 遞歸函數,包含備忘錄算法邏輯,改為void類型
void knapsack(int idx, int W, int N, int& maxVal) {// 基本情況if (idx == N || W == 0) {maxVal = 0;cout << "邊界:" << idx << " " << W << " " << maxVal << "\n";return;}// 檢查是否已經計算過if (dp[idx][W] != -1) {maxVal = dp[idx][W];cout << "已經計算過:" << idx << " " << W << " " << maxVal << "\n";return;}// 選擇不包含當前物品knapsack(idx + 1, W, N, maxVal);int without = maxVal; // 從上一次遞歸中獲取結果cout << "without:" << idx << " " << W << " " << without << "\n";int with = 0;// 選擇包含當前物品,如果背包容量足夠if (W >= weight[idx]) {knapsack(idx + 1, W - weight[idx], N, with);with = values[idx] + with; // 添加當前物品的價值cout << "with:" << idx << " " << W << " " << with << "\n";}// 計算最大價值并存儲備忘錄結果maxVal = max(without, with);dp[idx][W] = maxVal; // 存儲備忘錄結果//cout<<"idx=,W=,dp= "<<idx<<" "<<W<<" "<<dp[idx]
}*/struct memoFrame
{int index;int with;int without;int max_value;int capacity;int stage;
}stackMemo[N];void memoBag(int index, int capacity, vector<int>& weights, vector<int>& values)
{int tt = 0;stackMemo[++tt] = { 0,0,0,0,capacity,0 };int max_value = 0;while (tt > 0){//cout << "cnt=" << cnt << "\n";memoFrame& now = stackMemo[tt];//cout << "當前函數層為,index,capacity,stage=" << now.index << " " << now.capacity << " " << now.stage << "\n";if ((now.index == n || now.capacity <= 0)) {memoFrame& last = stackMemo[tt - 1];last.max_value = 0;//cout << "當前層為:,返回給上一層的返回值為" << now.index << " " << now.capacity << " " << last.max_value << "\n";tt--;//cout << "出棧:index,capacity,return" << now.index << " " << now.capacity << " " << last.max_value << "\n";continue;}if (dp[now.index][now.capacity] != -1){memoFrame& last = stackMemo[tt - 1];last.max_value = dp[now.index][now.capacity];//cout << "當前層為:,返回給上一層的返回值為" << now.index << " " << now.capacity << " " << last.max_value << "\n";tt--;//cout << "出棧:index,capacity,return" << now.index << " " << now.capacity << " " << last.max_value << "\n";continue;}if (now.stage == 0){stackMemo[++tt] = { now.index + 1,0,0,0,now.capacity,0 };//cout << "壓棧0:" << now.index + 1 << " " << now.capacity << " " << "\n";now.stage++;}else if (now.stage == 1){now.without = now.max_value;//cout << "更新without:index, without:" << now.index << " " << now.without << "\n";now.stage++;}else if (now.stage == 2){if (now.capacity >= weights[now.index]) stackMemo[++tt] = { now.index + 1, 0, 0, 0, now.capacity - weights[now.index], 0 };// cout << "壓棧1:" << now.index + 1 << " " << now.capacity << " " << "\n";now.stage++;}else if (now.stage == 3){if (now.capacity >= weights[now.index]){now.with = now.max_value + values[now.index];//cout << "更新with, index,with:" << now.index << " " << now.with << "\n";}now.stage++;}else if (now.stage == 4){memoFrame& last = stackMemo[tt - 1];dp[now.index][now.capacity] = max(now.with, now.without);for (int i = 0; i < n; i++){for (int j = 0; j < W; j++){cout << dp[i][j] << " ";}cout << "\n";}last.max_value = dp[now.index][now.capacity];Sleep(1000);//cout << "更新dp: index,dp:" << now.index << " " << last.max_value << "\n";tt--;//cout << "出棧:index,capacity,return" << now.index << " " << now.capacity << " " << last.max_value << "\n";}}}int main() {cin >> n >> W;; // 讀取物品數量和背包容量weights.resize(n);values.resize(n);for (int i = 0; i < n; ++i) {cin >> weights[i] >> values[i];}memset(dp, -1, sizeof(dp));memoBag(0, W, weights, values);cout << "最大價值:" << dp[0][W] << endl;return 0;
}/*
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*/
把三個題整合到一塊
#include <iostream>
#include <vector>
#include <cstring>
#include<iomanip>
#include <windows.h>using namespace std;const int N = 2e4 + 5;typedef long long LL;int n, W;//n可以是二分的數組長度,也可以是背包的物品個數,W是背包容量int ansPos=-1;//二分搜索到的答案位置int arr[N];int dp[505][1005]; // 備忘錄數組
vector<int> weights;
vector<int> values;struct binaryFrame {int l, r;int level;//記錄當前層數int step;//記錄步數
}stackBinary[N];struct backFrame
{int index;int current_weight;int current_value;int step;vector<int> chosenItems;int stage;
}stackBack[N];struct memoFrame
{int index;int with;int without;int max_value;int capacity;int stage;
}stackMemo[N];void binarySearch(int l, int r, int key)
{int nowLevel = 1, nowStep = 0, tt = 0, L = l, R = r;tt++;stackBinary[tt] = { l,r,nowLevel,nowStep };cout<<right<<setw(50) << "壓棧:" << "當前執行函數紙帶范圍為:(" << L << " , " << R << " )" << " 層數為" << nowLevel << " 執行步數為" << nowStep << "\n";Sleep(200);while (L < R){int mid = L + R >> 1;if (arr[mid] >= key){R = mid;stackBinary[++tt] = { L,R,++nowLevel,++nowStep };cout<<right<<setw(50) << "壓棧:" << "當前執行函數紙帶范圍為:(" << L << " , " << R << " )" << " 層數為" << nowLevel << " 執行步數為" << nowStep << "\n";Sleep(200);}else {L = mid + 1;stackBinary[++tt] = { L,R,++nowLevel,++nowStep };cout<<right<<setw(50) << "壓棧:" << "當前執行函數紙帶范圍為:(" << L << " , " << R << " )" << " 層數為" << nowLevel << " 執行步數為" << nowStep << "\n";Sleep(200);}}if (arr[R] == key) {ansPos = R;}while (tt > 0){cout<<right<<setw(50) << "出棧:" << "當前執行函數紙帶范圍為:(" << stackBinary[tt].l << " , " << stackBinary[tt].r << " )" << " 層數為" << stackBinary[tt].level << " 執行步數為" << stackBinary[tt].step << "\n";Sleep(200);tt--;}}void backBag(int n, int capacity, int& max_value, vector<int>& weights, vector<int>& values, vector<int>& chosenItems, vector<int>& best_set)
{int tt = 0, nowStep = 0;stackBack[++tt] = { 0,0,0,0,{},0 };cout<<right<<setw(50) << "壓棧:初始化壓棧,壓入 0 0 0 0 {} 0" << "\n";Sleep(200);while (tt > 0){backFrame now = stackBack[tt];cout << right << setw(50) << "當前執行函數層為:下標為:" << now.index << " 當前重量:" << now.current_weight << " 當前價值:" << now.current_value << " 當前步數:" << now.step << "\n";Sleep(200);if (stackBack[tt].index >= n) {if (stackBack[tt].current_value > max_value && stackBack[tt].current_weight <= capacity){max_value = stackBack[tt].current_value;best_set = stackBack[tt].chosenItems;}tt--;cout<<right<<setw(50) << "出棧1:出棧下標:" << now.index << " 當前重量:" << now.current_weight << " 當前價值:" << now.current_value << " 當前步數:" << now.step << "\n";Sleep(200);continue;}if (now.stage == 0) {//棧頂為初始狀態的話直接下一層函數壓棧chosenItems.push_back(now.index);stackBack[++tt] = { now.index + 1,now.current_weight + weights[now.index],now.current_value + values[now.index],now.step + 1,chosenItems,0 };cout<<right<<setw(50) << "壓棧1: 壓棧下標:" << now.index + 1 << " 壓棧重量:" << now.current_weight + weights[now.index] << " 壓棧價值:" << now.current_value + values[now.index] << " 壓棧步數:" << now.step + 1 << "\n";Sleep(200);stackBack[tt - 1].stage++;}else if (now.stage == 1) {chosenItems.pop_back();stackBack[++tt] = { now.index + 1,now.current_weight,now.current_value,now.step + 1,chosenItems,0 };cout<<right<<setw(50) << "壓棧2: 壓棧下標:" << now.index + 1 << " 壓棧重量:" << now.current_weight << " " << now.current_value << " " << now.step + 1 << "\n";Sleep(200);stackBack[tt - 1].stage++;}else if (now.stage == 2) {tt--;cout<<right<<setw(50) << "出棧2:" << now.index << " 出棧重量:" << now.current_weight << " 出棧價值:" << now.current_value << " 出棧步數" << now.step << "\n";Sleep(200);}}}void memoBag(int index, int capacity, vector<int>& weights, vector<int>& values)
{int tt = 0;stackMemo[++tt] = { 0,0,0,0,capacity,0 };int max_value = 0;while (tt > 0){memoFrame& now = stackMemo[tt];cout<<right<<setw(50) << "當前函數層為,當前執行下標:" << now.index << " 當前背包剩余容量:" << now.capacity << " 當前stage:" << now.stage << "\n";Sleep(200);if ((now.index == n || now.capacity <= 0)) {memoFrame& last = stackMemo[tt - 1];last.max_value = 0;//cout << "當前層為:,返回給上一層的返回值為" << now.index << " " << now.capacity << " " << last.max_value << "\n";tt--;cout<<right<<setw(50) << "出棧:出棧下標:" << now.index << " 出棧時剩余背包容量:" << now.capacity << " 出棧返回值:" << last.max_value << "\n";Sleep(200);continue;}if (dp[now.index][now.capacity] != -1){memoFrame& last = stackMemo[tt - 1];last.max_value = dp[now.index][now.capacity];//cout << "當前層為:,返回給上一層的返回值為" << now.index << " " << now.capacity << " " << last.max_value << "\n";tt--;cout<<right<<setw(50) << "出棧:出棧下標:" << now.index << " 出棧時剩余背包容量:" << now.capacity << " 出棧時返回值:" << last.max_value << "\n";Sleep(200);continue;}if (now.stage == 0){stackMemo[++tt] = { now.index + 1,0,0,0,now.capacity,0 };cout<<right<<setw(50) << "壓棧0:壓棧下標:" << now.index + 1 << " 壓棧背包容量;" << now.capacity << " " << "\n";Sleep(200);now.stage++;}else if (now.stage == 1){now.without = now.max_value;//cout << "更新without:index, without:" << now.index << " " << now.without << "\n";now.stage++;}else if (now.stage == 2){if (now.capacity >= weights[now.index]) stackMemo[++tt] = { now.index + 1, 0, 0, 0, now.capacity - weights[now.index], 0 };cout<<right<<setw(50) << "壓棧1:壓棧下標:" << now.index + 1 << " 壓棧背包容量:" << now.capacity-weights[now.index] << " " << "\n";Sleep(200);now.stage++;}else if (now.stage == 3){if (now.capacity >= weights[now.index]){now.with = now.max_value + values[now.index];//cout << "更新with, index,with:" << now.index << " " << now.with << "\n";}now.stage++;}else if (now.stage == 4){memoFrame& last = stackMemo[tt - 1];dp[now.index][now.capacity] = max(now.with, now.without);last.max_value = dp[now.index][now.capacity];//cout << "更新dp: index,dp:" << now.index << " " << last.max_value << "\n";tt--;cout<<right<<setw(50) << "出棧:出棧下標:" << now.index << " 出棧時背包容量:" << now.capacity << " 這一層出棧的返回值:" << last.max_value << "\n";Sleep(200);}}}int main()
{int op;cout<<right<<setw(50) << "請選擇要執行的遞歸函數模擬:1.二分搜索,2.回溯法,3.備忘錄法\n";while(cin >> op) {if (op == 1) {int key;cout << right << setw(50) << "棧模擬遞歸二分算法\n\n\n";cout << right << setw(50) << "請輸入查詢數組長度\n";cin >> n;cout << right << setw(50) << "請輸入" << n << "個數字\n";for (int i = 0; i < n; i++){cin >> arr[i];}cout << right << setw(50) << "請輸入需要查找的數字key\n";cin >> key;binarySearch(0, n - 1, key);if (ansPos == -1) cout << right << setw(50) << "找不到這個吊數\n";else cout << right << setw(50) << "數字" << key << "在數組中的第" << ansPos + 1 << "個位置\n";}else if (op == 2){weights.clear();values.clear();cout << right << setw(50) << "棧模擬遞歸回溯算法\n\n\n";cout << right << setw(50) << "請輸入物品件數和背包容量\n";cin >> n >> W;cout << right << setw(50) << "請輸入" << n << "件物品的質量和價值\n";for (int i = 0; i < n; i++){int x, y;cin >> x >> y;weights.push_back(x);values.push_back(y);}int max_value = -1;vector<int> best_set;vector<int> chosenItems;backBag(n, W, max_value, weights, values, chosenItems, best_set);cout << right << setw(50) << "可以獲得的最大價值為:" << max_value << "\n";for (auto i : best_set){cout << right << setw(50) << "選擇了第" << i + 1 << "件物品\n";}}else if (op == 3){weights.clear();values.clear();cout << right << setw(50) << "棧模擬遞歸備忘錄算法\n\n\n";cout << right << setw(50) << "請輸入物品件數和背包容量\n";cin >> n >> W;cout << right << setw(50) << "請輸入" << n << "件物品的質量和價值\n";for (int i = 0; i < n; i++){int x, y;cin >> x >> y;weights.push_back(x);values.push_back(y);}memset(dp, -1, sizeof(dp));memoBag(0, W, weights, values);cout << right << setw(50) << "能獲得的最大價值為:" << dp[0][W] << "\n";}cout << right << setw(50) << "1.繼續,2.結束\n";cin >> op;if (op == 2) break;cout << right << setw(50) << "請選擇要執行的遞歸函數模擬:1.二分搜索,2.回溯法,3.備忘錄法\n";}return 0;
}/*二分搜索樣例輸入
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*//*回溯與備忘錄樣例輸入
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*//*需要模擬的二分遞歸函數
int erfen(int arr[], int l, int r, int key)
{int ans = -1;int mid = l + r >> 1;if (arr[mid] == key && l == r) return r;if (l >= r) return -1;if (arr[mid] >= key) {ans = erfen(arr, l, mid, key);}else {ans = erfen(arr, mid + 1, r, key);}return ans;
}
*//*
// 需要模擬的遞歸回溯函數
void knapsack(int index, int current_weight, int current_value, int capacity, const vector<int>& weights, const vector<int>& values, vector<int>& chosen_items) {// 基礎情況:如果考慮完所有物品if (index == weights.size()) {// 檢查當前物品集合是否是一個有效解if (current_weight <= capacity && current_value > max_value) {max_value = current_value;best_set = chosen_items;}return;}// 選擇當前物品chosen_items.push_back(index);knapsack(index + 1, current_weight + weights[index], current_value + values[index], capacity, weights, values, chosen_items);chosen_items.pop_back(); // 回溯// 不選擇當前物品knapsack(index + 1, current_weight, current_value, capacity, weights, values, chosen_items);
}*//*需要模擬的備忘錄遞歸函數
// 遞歸函數,包含備忘錄算法邏輯,改為void類型
void knapsack(int idx, int W, int N, int& maxVal) {// 基本情況if (idx == N || W == 0) {maxVal = 0;cout << "邊界:" << idx << " " << W << " " << maxVal << "\n";return;}// 檢查是否已經計算過if (dp[idx][W] != -1) {maxVal = dp[idx][W];cout << "已經計算過:" << idx << " " << W << " " << maxVal << "\n";return;}// 選擇不包含當前物品knapsack(idx + 1, W, N, maxVal);int without = maxVal; // 從上一次遞歸中獲取結果cout << "without:" << idx << " " << W << " " << without << "\n";int with = 0;// 選擇包含當前物品,如果背包容量足夠if (W >= weight[idx]) {knapsack(idx + 1, W - weight[idx], N, with);with = values[idx] + with; // 添加當前物品的價值cout << "with:" << idx << " " << W << " " << with << "\n";}// 計算最大價值并存儲備忘錄結果maxVal = max(without, with);dp[idx][W] = maxVal; // 存儲備忘錄結果//cout<<"idx=,W=,dp= "<<idx<<" "<<W<<" "<<dp[idx]
}*/