B. Santa Claus and Keyboard Check 模拟

http://codeforces.com/contest/752/problem/B

uuu

yyu

xy

xx

注意变化了之后，检查一次前面已经变化过的就好。因为可能前面的满足，但是变了后不满足。

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <assert.h>
#define IOS ios::sync_with_stdio(false)
using namespace std;
#define inf (0x3f3f3f3f)
typedef long long int LL;

#include <iostream>
#include <sstream>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <string>

const int maxn = 1e3 + ;
struct node {
    char x, y;
    node(char xx, char yy) {
        if (xx > yy) {
            swap(xx, yy);
        }
        x = xx;
        y = yy;
    }
    bool operator < (const struct node & rhs) const {
        if (x != rhs.x) return x < rhs.x;
        else return y < rhs.y;
    }
};
set<struct node>ans;
char str[maxn];
char sub[maxn];
char book[maxn];
bool vis[maxn];
void work() {
    memset(book, '$', sizeof book);
    cin >> str + ;
    cin >> sub + ;
    for (int i = ; sub[i]; ++i) book[sub[i]] = sub[i];
    for (int i = ; str[i]; ++i) {
        if (str[i] != book[sub[i]]) {
            char ch = book[sub[i]];
            book[book[sub[i]]] = str[i];
            book[str[i]] = ch;
            ans.insert(node(str[i], sub[i]));
            for (int j = ; j <= i; ++j) {
                if (str[j] != book[sub[j]]) {
//                    cout << i << endl;
                    cout << - << endl;
                    return;
                }
            }
        }
    }
    cout << ans.size() << endl;
    for (set<struct node> :: iterator it  = ans.begin(); it != ans.end(); ++it) {
        cout << it->x << " " << it->y << endl;
    }
}

int main() {
#ifdef local
    freopen("data.txt", "r", stdin);
//    freopen("data.txt", "w", stdout);
#endif
    work();
    return ;
}