暴力和记忆化各调了多少次
十件小物品、容量 8。一边纯暴力递归,一边加上记忆化。运行下面这段程序:
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
using namespace std;
using Item = pair<int, int>; // (重量, 价值)
const vector<Item> ITEMS = {{3, 8}, {4, 9}, {5, 11}};
const vector<Item> IT = {{1, 1}, {2, 3}, {1, 2}, {2, 2}, {1, 1}, {2, 4}, {1, 3}, {2, 2}, {1, 1}, {2, 3}};
long long calls = 0;
int go_rec(int i, int c) {
calls++;
if (i == (int)IT.size()) return 0;
auto [w, v] = IT[i];
int best = go_rec(i + 1, c);
if (c >= w) {
int take = go_rec(i + 1, c - w) + v;
if (take > best) best = take;
}
return best;
}
vector<vector<int>> memo;
int go_memo(int i, int c) {
calls++;
if (memo[i][c] != -1) return memo[i][c];
if (i == (int)IT.size()) return 0;
auto [w, v] = IT[i];
int best = go_memo(i + 1, c);
if (c >= w) {
int take = go_memo(i + 1, c - w) + v;
if (take > best) best = take;
}
memo[i][c] = best;
return best;
}
int main() {
calls = 0;
go_rec(0, 8);
long long a = calls;
calls = 0;
memo.assign(IT.size() + 1, vector<int>(9, -1));
go_memo(0, 8);
cout << a << "/" << calls << endl;
}
(本题用 g++ -std=c++17 -O0 编译。)
全部评论