这道题要考虑一些细节。

当要交换位置的时候，X与Y相邻需要特殊处理。


#include<iostream>
#include<cstdio>
#include<cstring>
#define MAXN 100200
using namespace std;

long long Right[MAXN], Lift[MAXN];

void link(int X, int Y) {
    Right[X] = Y;
    Lift[Y] = X;
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("in.txt", "r", stdin);
#endif // ONLINE_JUDGE
    int n, m, Case = 0;
    while(cin >> n >> m) {
        memset(Lift, 0, sizeof(Lift));
        memset(Right, 0, sizeof(Right));
        bool inx = false;
        long long sum = 0, cur = 0;
        for(int i = 1; i <= n; i++) {
            link(i, i + 1);
            link(i - 1, i);
        }
        while(m--) {
            int cmd, X, Y;
            cin >> cmd;
            if(cmd == 4) {
                inx = !inx;
                continue;
            }
            cin >> X >> Y;
            if(cmd == 3&&(Right[Y] == X)) swap(X, Y);
            if(cmd != 3&& inx) cmd = 3 - cmd;
            if(cmd == 1&& Lift[Y] == X) continue;
            if(cmd == 2&& Right[Y] == X) continue;
            int XL = Lift[X], XR = Right[X], YL = Lift[Y], YR = Right[Y];
            if(cmd == 3) {
                if(Right[X] == Y) {
                    link(XL, Y);
                    link(Y, X);
                    link(X, YR);
                } else {
                    link(X, YR);
                    link(YL, X);
                    link(Y, XR);
                    link(XL, Y);
                }
            } else if(cmd == 2) {
                link(Y, X);
                link(X, YR);
                link(XL, XR);
            } else if(cmd == 1) {
                link(XL, XR);
                link(YL, X);
                link(X, Y);
            }
        }
        for(int i = 1; i <= n; i++) {
            cur = Right[cur];
            if(i & 1) sum += cur;
        }
        if(inx&& !(n & 1)) sum = (long long)n / 2 * (n + 1) - sum;
        printf("Case %d: %lld\n", ++Case, sum);
    }
    return 0;
}