关于BFS与DFS

2024/7/18

电路维修

双端队列BFS

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define haha puts("")
#define ye puts("Yes")
#define no puts("No")
typedef pair<int, int> pii;
typedef unsigned long long ull;
const int N = 3e5 + 10;
const int M = 1010;
const double eps = 1e-8;
int dx[] = {-1, -1, 1, 1};
int dy[] = {-1, 1, 1, -1};
int n, m, k;
int ksm(int x, int y) {
	int ans = 1;
	while (y) {
		if (y & 1)
			ans = ans * x;
		y >>= 1;
		x = x * x;
	}
	return ans;
}
char a[M][M];
int dis[M][M];
int g[M][M];
char cp[] = {'\\', '/', '\\', '/'};
int ix[4] = {-1, -1, 0, 0};
int iy[4] = {-1, 0, 0, -1};
void bfs() {
	memset(dis, 0x3f3f3f3f, sizeof dis);
	deque<pii> dq;
	dq.push_back({0, 0});
	dis[0][0] = 0;
	while (dq.size()) {
		auto t = dq.front();
		dq.pop_front();
		int x = t.first, y = t.second;
		for (int i = 0; i < 4; i++) {
			int xx = x + dx[i];
			int yy = y + dy[i];
			if (xx >= 0 && xx <= n && yy >= 0 && yy <= m) {
				int fx = x + ix[i], fy = y + iy[i];
				int w = 0;
				if (a[fx][fy] != cp[i]) w = 1;
				if (dis[xx][yy] > dis[x][y] + w) {
					dis[xx][yy] = dis[x][y] + w;
					if (w == 1) dq.push_back({xx, yy});
					else dq.push_front({xx, yy});
				}
			}
		}
	}
	if (dis[n][m] > 1e18)
		cout << "NO SOLUTION\n";
	else
		cout << dis[n][m] << '\n';
}
void solve() {
	cin >> n >> m;
	for (int i = 0; i < n; i++) {
		scanf("%s", &a[i]);
	}
	bfs();
}

signed main() {
//	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	int t = 1;
//	cin >> t;
	while (t--)
		solve();
}

记录一下\(2^n\)选点排列的\(dfs\)代码

void dfs(int u, int x) {
	a[u] = x;
	if (u == n) {

	}
	dfs(u + 1, 0);
	dfs(u + 1, 1);
}
dfs(0,0)

P3052 [USACO12MAR] Cows in a Skyscraper G

#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N = 1e6 + 10;
int n, m;
vector<int> a;
bool st[100];
int b[100];
int mx = 0;
int ab[100];


void dfs(int u, int x) {
	b[u] = x;
	if (u == a.size()) {
//		for (int i = 1; i <= a.size(); i++) {
//			cout << b[i] << ' ';
//		}
//		cout << '\n';
		int sum = 0;
		//求和
		for (int i = 0; i < a.size(); i++) {
			if (b[i + 1] == 1) {
				sum += a[i];
			}
		}
		//如果能行就找最大可能
		if (sum <= m && sum > mx) {
			mx = sum;
			for (int i = 0; i <= 99; i++) ab[i] = 0;
			//更新a数组的值
			for (int i = 0; i < a.size(); i++) {
				if (b[i + 1] == 1) ab[i + 1] = 1;
			}
		}
		return;
	}
	dfs(u + 1, 0);
	dfs(u + 1, 1);
}
signed main() {
	cin >> n >> m;
	for (int i = 0; i < n; i++) {
		int x;
		cin >> x;
		a.push_back(x);
	}
	int f = 0;
	while (1) {
		f ++;
		mx = 0;
		for (int i = 1; i <= n; i++) st[i] = 0;
		dfs(0, 0);
		vector<int> ca;
		for (int i = 0; i < a.size(); i++) {
			if (ab[i + 1] == 0)
				ca.push_back(a[i]);
		}
		a = ca;
		if (a.size() == 0) break;
	}
	cout << f << '\n';
}