题目链接：uva 1385 - Billing Tables

题目大意：给定n个电话前缀，每个前缀是一个区域的前缀，现在要生成一个新的电话单，即对于每个电话号码，从旧的电话单上从前向后遍历，如果出现前缀匹配，则该电话号码对应的即为当前的区号，要求生成的新电话单尽量小。

解题思路：用dfs建立字典树，在区间范围内的点对应均为对应的区号，注意如果70、71、72、...79都为SB的话，那么可以合并成7，并且对应区号为SB。
注意合并的条件为区号相同即可，并不是说对应旧电话单匹配位置相同。
注意这组数据：0 - 9 all

#include <cstdio>
#include <cstring>
#include <vector>
#include <string>
#include <map>
#include <iostream>
#include <algorithm>

using namespace std;
const int sigma_size = 10;
typedef pair<string, string> pii;

struct Node {
    int val;
    Node* next[sigma_size];

    Node() { 
        val = 0;
        memset(next, 0, sizeof(next));
    }
};

void clear(Node* &p);
void insert (Node* &p, int d, int L, int R, int tig);
void dfs(Node* p, string str);
int pushup(Node* &p, int tig);

map<string, int> g;

int n, m;
string l, r, name[105];
Node* root = NULL;

vector<pii> vec;

void init () {
    vec.clear();
    g.clear();
    string tmp;

    for (int i = 1; i <= m; i++) {
        cin >> l >> tmp >> r >> name[i];

        tmp = "";
        int d = l.length() - r.length();

        for (int i = 0; i < d; i++)
            tmp += l[i];
        tmp += r;
        r = tmp;

        if (l > r)
            continue;

        int k = i;
        if (g.count(name[i]))
            k = g[name[i]];
        else
            g[name[i]] = i;

        insert(root, 0, 1, 1, k);
    }
}

int main () {
    int cas = 0;
    while (cin >> m) {
        if (cas++)
            cout << endl;

        init();
        pushup(root, m+1);
        dfs(root, "");
        clear(root);

        printf("%lu\n", vec.size());
        for (int i = 0; i < vec.size(); i++)
            cout << vec[i].first << " " << vec[i].second << endl;
    }
    return 0;
}

int pushup (Node* &p, int tig) {
    if (p == NULL) {
        p = new Node;
        return p->val = tig;
    }

    if (p->val)
        tig = p->val;

    int k = pushup(p->next[0], tig);
    for (int i = 1; i < sigma_size; i++) {
        if (k != pushup(p->next[i], tig))
            k = 0;
    }

    return p->val = k;
}

void dfs (Node* p, string str) {
    if (p != root && p->val) {
        if (p->val <= m && name[p->val] !=  "invalid")
            vec.push_back(make_pair(str, name[p->val]));
        return ;
    }

    for (int i = 0; i < sigma_size; i++) {
        if (p->next[i] != NULL) {
            char ch = ‘0‘ + i;
            dfs(p->next[i], str + ch);
        }
    }
}

void insert (Node* &p, int d, int L, int R, int tig) {
    if (p == NULL)
        p = new Node;

    if (p->val)
        tig = p->val;

    if (d >= l.length()) {
        p->val = tig;
        return;
    }

    if (L == 0 && R == 0) {
        p->val = tig;
        return;
    } else if (L == 0) {
        insert(p->next[r[d]-‘0‘], d + 1, 0, 1, tig);
        for (int i = 0; ‘0‘ + i < r[d]; i++)
            insert(p->next[i], d + 1, 0, 0, tig);
    } else if (R == 0) {
        insert(p->next[l[d]-‘0‘], d + 1, 1, 0, tig);
        for (int i = l[d] - ‘0‘ + 1; i < sigma_size; i++)
            insert(p->next[i], d + 1, 0, 0, tig);
    } else if (r[d] == l[d]) {
        insert(p->next[l[d]-‘0‘], d + 1, 1, 1, tig);
    } else {
        insert(p->next[l[d]-‘0‘], d + 1, 1, 0, tig);
        insert(p->next[r[d]-‘0‘], d + 1, 0, 1, tig);
        for (int i = l[d] + 1; i < r[d]; i++)
            insert(p->next[i-‘0‘], d + 1, 0, 0, tig);
    }
}

void clear(Node* &p) {
    for (int i = 0; i < sigma_size; i++) {
        if (p->next[i] != NULL)
            clear(p->next[i]);
    }
    delete p;
    p = NULL;
}

uva 1385 - Billing Tables(字典树)