两种写法算得一样吗
二维写法取 dp[3][10],一维写法取 dp[10]。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}};
vector<vector<long long>> knap2d(const vector<Item>& items, int cap) {
int n = items.size();
vector<vector<long long>> dp(n + 1, vector<long long>(cap + 1, 0));
for (int i = 1; i <= n; i++) {
auto [w, v] = items[i - 1];
for (int c = 0; c <= cap; c++) {
dp[i][c] = dp[i - 1][c];
if (c >= w && dp[i - 1][c - w] + v > dp[i][c]) dp[i][c] = dp[i - 1][c - w] + v;
}
}
return dp;
}
vector<long long> knap1d(const vector<Item>& items, int cap) {
vector<long long> dp(cap + 1, 0);
for (auto [w, v] : items) {
for (int c = cap; c >= w; c--) {
if (dp[c - w] + v > dp[c]) dp[c] = dp[c - w] + v;
}
}
return dp;
}
int main() {
cout << knap2d(ITEMS, 10)[3][10] << "/" << knap1d(ITEMS, 10)[10] << endl;
}
(本题用 g++ -std=c++17 -O0 编译。)
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