1.19

FBI树

[P1087 NOIP2004 普及组] FBI 树 - 洛谷 | 计算机科学教育新生态 (luogu.com.cn)

• 不用去建树，直接不断拆分递归，然后每次判断一下这个区间内有多少个1，0.
• 感觉类似二分

import java.util.Scanner;

public class Main {
    static int n;
    static String s;
    public static void dfs(int up, int down) {
    	if(up != down) {
    		int mid = (up + down) / 2;
    		dfs(up, mid);
    		dfs(mid + 1, down);
    	}
    	
    	int num_1 = 0;
    	int num_0 = 0;
    	for(int i = up; i <= down; i++) {
    		if(s.charAt(i) == '1') {
    			num_1++;
    		} else {
    			num_0++;
    		}
    	}
    	
    	if(num_1 != 0 && num_0 != 0) {
    		System.out.print("F");
    	}else if(num_1 != 0){
    		System.out.print("I");
    	}else {
    		System.out.print("B");
    	}
    }
    
    public static void main(String[] args) {
    	Scanner scanner = new Scanner(System.in);
    	n = scanner.nextInt();
    	s = scanner.next();
    	s = " " + s;
    	dfs(1, s.length() - 1);
    	
    	return;
	}
}

#include<iostream>
#include<string>
using namespace std;

int n;
string s;

void dfs(int up, int down) {
	if(up != down) {
		int mid = (up + down) / 2;
		dfs(up, mid);
		dfs(mid + 1, down);
	}
	
	int num_1 = 0;
	int num_0 = 0;
	for(int i = up; i <= down; i++) {
		if(s[i] == '1') {
			num_1++;
		} else {
			num_0++;
		}
	}
	
	if(num_1 && num_0) {
		cout<<"F";
	}else if(num_1){
		cout<<"I";
	}else {
		cout<<"B";
	}
	
	 
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	
	cin>>n>>s;
	
	s = " " + s;
	dfs(1, s.size() - 1);
	
	return 0;
}

01迷宫

P1141 01迷宫 - 洛谷 | 计算机科学教育新生态 (luogu.com.cn)

• 本题一开始用的dfs来了一发，但是发现有几个点会爆TLE，考虑优化方案。
• 考虑到就是，如果我能从一个块走到另一个块，那么我必然可以走回去。
• 即其实就是一个染色连通块，只要已经染过色，就已经产生了答案，也就是不必再去搜索。
• 那之后就比较简单了，我们只需要把走过的点标记然后下次遇到走过的点不搜就是了
• 至于染色块答案存储，选用的时map

#include<iostream>
#include<cstring>
#include<map>
using namespace std;

const int N = 1e3 + 10;
int g[N][N]; 
bool str[N][N];
int cnt[N][N];
int cnt_bankuai;
int n, m;
int ans;
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
map<int,int>myMap;

void dfs(int x, int y) {
	for(int i = 0; i < 4; i++) {
		int nowx = dx[i] + x;
		int nowy = dy[i] + y;
		if(nowx >= 1 && nowx <= n && nowy >= 1 && nowy <= n) {
			if(!str[nowx][nowy] && g[nowx][nowy] == !g[x][y]) {
				str[nowx][nowy] = true;
				cnt[nowx][nowy] = cnt_bankuai;
				myMap[cnt_bankuai]++;
				ans++;
				dfs(nowx, nowy);
			}
		}
		
	}
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	
	cin>>n>>m;
	
	for(int i = 1; i <= n; i++) {
		string s;
		cin>>s;
		for(int j = 1;j <= n; j++) {
			g[i][j] = s[j - 1] - '0';
		}
	}
	
	while(m--) {
		//memset(str, false, sizeof(str));
		ans = 1;
		int x, y;
		cin>>x>>y;

		if(!str[x][y]) {
			cnt_bankuai++;
			myMap[cnt_bankuai]++;
			cnt[x][y] = cnt_bankuai;
			str[x][y] = true;
			dfs(x, y);
		}else{
			int num = cnt[x][y];
			ans = myMap[num];
		}
		

		cout<<ans<<endl;
	}
	
	return 0;
}

package shuati;

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {
	
	static final int N = 1010;
	static int[][] g = new int[N][N];
	static boolean[][] str = new boolean[N][N];
	static int[][]cnt = new int[N][N];
	static int dx[] = {1, 0, -1, 0};
	static int dy[] = {0, 1, 0, -1};
    static int n, m, ans, cnt_bankuai;
    static Map<Integer, Integer>myMap = new HashMap<Integer, Integer>();
    
    public static void dfs(int x, int y) {
    	for(int i = 0; i < 4; i++) {
    		int nowx = dx[i] + x;
    		int nowy = dy[i] + y;
    		if(nowx >= 1 && nowx <= n && nowy >= 1 && nowy <= n) {
    			if(!str[nowx][nowy] && ((g[nowx][nowy] == g[x][y] + 1) ||( g[nowx][nowy] == g[x][y] - 1))) {
    				str[nowx][nowy] = true;
    				cnt[nowx][nowy] = cnt_bankuai;
    				myMap.put(cnt_bankuai, myMap.get(cnt_bankuai) + 1);
    				ans++;
    				dfs(nowx, nowy);
    			}
    		}
    		
    	}
    }
    
    public static void main(String[] args) {
    	Scanner scanner = new Scanner(System.in);
    	n = scanner.nextInt();
    	m = scanner.nextInt();
    	
    	for(int i = 1; i <= n; i++) {
    		String s;
    		s = scanner.next();
    		for(int j = 1;j <= n; j++) {
    			g[i][j] = s.charAt(j - 1) - '0';
    		}
    	}
    	
    	while(m-- != 0) {
    		ans = 1;
    		int x, y;
    		x = scanner.nextInt();
    		y = scanner.nextInt();

    		if(!str[x][y]) {
    			cnt_bankuai++;
    			myMap.put(cnt_bankuai, 1);
    			cnt[x][y] = cnt_bankuai;
    			str[x][y] = true;
    			dfs(x, y);
    		}else{
    			int num = cnt[x][y];
    			ans = myMap.get(num);
    		}
    		

    		System.out.println(ans);
    	}
    	
    	return;
	}
}

• java的这个代码会爆栈溢出，不知道怎么调了
• 今晚还有场div3，✌