hihoCoder 1228 Mission Impossible 6(模拟)

题目链接：hihoCoder 1228 Mission Impossible 6

解题思路

纯模拟，因为限制了字符串的长度，所以时间上可以接受。

代码

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

using namespace std;
const int maxn = 1e4 + 5;

struct Stack {
    int n;
    char s[maxn];

    void push(char ch) { s[n++] = ch; }
    void pop() { n--; }
    bool empty() { return n == 0; }
}L, R;

int N, M, P, E;
bool rewrite, iscopy;
char order[maxn], text[maxn];

void init () {
    E = L.n = R.n = 0;
    rewrite = iscopy = false;
    scanf("%d%s", &M, order);
    N = strlen(order);
}

void moveLeft () { 
    if (!L.empty()) {
        R.push(L.s[--L.n]);
        if (iscopy) P++;
    }
}

void moveRight () { 
    if (!R.empty()) {
        L.push(R.s[--R.n]);
        if (iscopy) P--;
    }
}

void deleteBlock() {
    if (P < 0) {
        P = -P;
        for (int i = 1; i <= P; i++)
            L.pop();
    } else
        for (int i = 1; i <= P; i++)
            R.pop();
}

void deleteLeft () {
    if (!L.empty()) L.pop();
    iscopy = false;
}

void deleteRight () {
    if (iscopy) deleteBlock();
    else if (!R.empty()) R.pop();
    iscopy = false;
}

void select () {
    if (iscopy) {
        E = 0;
        if (P < 0) {
            P = -P;
            for (int i = 0; i < P; i++)
                text[E++] = L.s[L.n-P+i];
        } else {
            for (int i = 1; i <= P; i++)
                text[E++] = R.s[R.n-i];
        }
    // printf("%d %d!\n", P, E);
        iscopy = false;
    } else {
        iscopy = true;
        P = 0;
    }
}

void write (char ch) {
    if (rewrite && !R.empty()) R.pop();
    if (L.n + R.n + 1 > M) return;
    L.push(ch);
    iscopy = false;
}

void copy () {
    int pos = L.n + R.n + E;
    if (rewrite) pos -= R.n;
    if (pos > M) return;
    for (int i = 0; i < E; i++)
        write(text[i]);
    iscopy = false;
}

void solve () {
    for (int i = 0; i < N; i++) {
        char& ch = order[i];
        if (ch == 'L')
            moveLeft();
        else if (ch == 'R')
            moveRight();
        else if (ch == 'S') {
            rewrite ^= true; 
            iscopy = false;
        } else if (ch == 'B')
            deleteLeft();
        else if (ch == 'D')
            deleteRight();
        else if (ch == 'C') {
            select();
        } else if (ch == 'V')
            copy();
        else if (ch >= 'a' && ch <= 'z')
            write(ch);
    }
}

int main () {
    int cas;
    scanf("%d", &cas);
    while (cas--) {
        init();
        solve();
        if (L.empty() && R.empty()) printf("NOTHING\n");
        else {
            for (int i = 0; i < L.n; i++) printf("%c", L.s[i]);
            for (int i = R.n-1; i >= 0; i--) printf("%c", R.s[i]);
            printf("\n");
        }
    }
    return 0;
}