2016"百度之星" - 资格赛（Astar Round1）

逆元 1001 Problem A

求前缀哈希和逆元

#include <bits/stdc++.h>

typedef long long ll;
const int MOD = 9973;
const int N = 1e5 + 5;
int inv[MOD+5];
int ha[N];
char str[N];
int n;

void Inv(int n, int p) {
    inv[1] = 1;
    for (int i=2; i<=n; ++i) {
        inv[i] = (ll) (p - p / i) * inv[p%i] % p;
    }
}

void init_hash() {
    ha[0] = 1;
    for (int i=1; i<=n; ++i) {
        ha[i] = (ll) ha[i-1] * (str[i] - 28) % MOD;
    }
}

int main() {
    Inv (MOD, MOD);
    int q;
    while (scanf ("%d", &q) == 1) {
        scanf ("%s", str + 1);
        n = strlen (str + 1);
        init_hash ();
        for (int i=0; i<q; ++i) {
            int l, r; scanf ("%d%d", &l, &r);
            printf ("%d\n", (ll) ha[r] * inv[ha[l-1]] % MOD);
        }
    }
    return 0;
}

dp 1002 Problem B

状态转移方程：dp[i] = dp[i-1] + dp[i-2]，Java写大数

import java.math.*;
import java.io.*;
import java.util.*;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		BigInteger[] dp = new BigInteger[205];
		dp[1] = BigInteger.ONE;
		dp[2] = BigInteger.ONE.add(BigInteger.ONE);
		for (int i=3; i<=200; ++i) {
			dp[i] = dp[i-1].add(dp[i-2]);
		}

		Scanner cin = new Scanner (System.in);
		int n;
		while (cin.hasNext ()) {
			n = cin.nextInt ();
			System.out.println (dp[n]);
		}
	}

	static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }
    }

}

字典树 1003 Problem C

1、insert : 往神奇字典中插入一个单词

2、delete: 在神奇字典中删除所有前缀等于给定字符串的单词

3、search: 查询是否在神奇字典中有一个字符串的前缀等于给定的字符串

字典树删除操作，按出现的次数，在前缀路径上依次删除，最后的扩展结点清空．

#include <cstdio>
#include <cstring>
#include <algorithm>

const int N = 1e5 + 5;
char oper[10];
char str[35];
const int NODE = N * 30;
struct Trie {
    int ch[NODE][26], val[NODE];
    int sz;
    void clear() {
        memset (ch[0], 0, sizeof (ch[0]));
        sz = 1;
    }
    int idx(char c) {
        return c - 'a';
    }
    void insert(char *s) {
        int u = 0;
        for (int c, i=0; s[i]; ++i) {
            c = idx (s[i]);
            if (!ch[u][c]) {
                memset (ch[sz], 0, sizeof (ch[sz]));
                val[sz] = 0;
                ch[u][c] = sz++;
            }
            u = ch[u][c];
            val[u]++;
        }
    }
    void del(char *s, int num) {
        int u = 0;
        for (int c, i=0; s[i]; ++i) {
            c = idx (s[i]);
            u = ch[u][c];
            val[u] -= num;
        }
        memset (ch[u], 0, sizeof (ch[u]));
    }
    int _search(char *t) {
        int u = 0;
        for (int c, i=0; t[i]; ++i) {
            c = idx (t[i]);
            if (!ch[u][c]) {
                return 0;
            }
            u = ch[u][c];
        }
        return val[u];
    }
};
Trie trie;

int main() {
    int n;
    while (scanf ("%d", &n) == 1) {
        trie.clear ();
        for (int i=0; i<n; ++i) {
            scanf ("%s%s", oper, str);
            if (oper[0] == 'i') {
                trie.insert (str);
            } else if (oper[0] == 'd') {
                int cnt = trie._search (str);
                if (cnt > 0) {
                    trie.del (str, cnt);
                }
            } else {
                int cnt = trie._search (str);
                if (cnt > 0) {
                    puts ("Yes");
                } else {
                    puts ("No");
                }
            }
        }
    }
    return 0;
}

STL 1004 Problem D

map或者双hash

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

const int N = 1e6 + 10;
const int MOD = 1e9 + 7;
char str[45];
int a[45];
std::map<string, int> mp;

int main() {
    int n; scanf ("%d", &n);
    mp.clear ();
    string str;
    for (int i=0; i<n; ++i) {
        cin >> str;
        sort (str.begin (), str.end ());
        printf ("%d\n", mp[str]);
        mp[str]++;
    }
    return 0;
}