1018 Public Bike Management 结题记录（dfs剪枝）

个人觉得直接放入代码是最管用的。
其他方法类似，题意请参考其他博主。

#include <bits/stdc++.h>
using namespace std;
const int N = 1e4 + 50;int maxn = 2000000000;
int c, n, ed, s[N], m, minlen, needn, backn, pre[N];
bool flag, book[N];
vector<pair<int, int > > e[N];inline void dfs(int u, int points, int maxneed, int stores, int len)
{if (len > minlen) return ;int nd = points * c / 2 - stores;maxneed = max(maxneed, max(0, nd));if (u == ed) {int tneedn, tbackn;if (nd <= 0) {// dont needtneedn = maxneed; tbackn = -nd + maxneed;} else {// need;tneedn = max(maxneed, nd); tbackn = 0;}if (len == minlen) {if (needn > tneedn || (needn == tneedn && backn > tbackn)) {needn = tneedn; backn = tbackn;} } else if (minlen > len) {minlen = len; needn = tneedn; backn = tbackn;}return ;}for (int i = 0; i < e[u].size(); i++) {int v = e[u][i].first, w = e[u][i].second;if (book[v]) continue;book[v] = true;dfs(v, points + 1, maxneed, stores + s[v], len + w);book[v] = false;}
}inline void dfs2(int u, int points, int maxneed, int stores, int len)
{if (flag) return ;if (len > minlen) return ;int nd = points * c / 2 - stores;maxneed = max(maxneed, max(0, nd));if (u == ed) {int tneedn, tbackn;if (nd <= 0) {// dont needtneedn = maxneed; tbackn = -nd + maxneed;} else {// need;tneedn = max(maxneed, nd); tbackn = 0;}if (len == minlen) {if (tneedn == needn && tbackn == backn) {// puts("test 1");flag = true;}} return ;}for (int i = 0; i < e[u].size(); i++) {int v = e[u][i].first, w = e[u][i].second;if (book[v]) continue;book[v] = true;pre[v] = u;dfs2(v, points + 1, maxneed, stores + s[v], len + w);if (flag) return ;book[v] = false;}
}signed main()
{scanf("%d%d%d%d", &c, &n, &ed, &m);for (int i = 1; i <= n; i++) scanf("%d", &s[i]);while (m--) {int u, v, w; scanf("%d%d%d", &u, &v, &w);e[u].push_back({v, w});e[v].push_back({u, w});}minlen = maxn, needn = maxn, backn = maxn;book[0] = true;dfs(0, 0, 0, 0, 0);// printf("%d %d %d\n", minlen, needn, backn);memset(book, 0, sizeof book);book[0] = true;dfs2(0, 0, 0, 0, 0);vector<int > res;while (ed != 0) {res.push_back(ed); ed = pre[ed];}printf("%d %d", needn, 0);for (int i = res.size() - 1; i >= 0; i--) {printf("->%d", res[i]);}printf(" %d\n", backn);return 0;
}