UVa 12657 Boxes in a Line 双向链表

#include<cstdio>
using namespace std;
int left[100010], right[100010];
int main() {
	int n, m, times(0);
	while (scanf("%d%d", &n, &m) == 2) {
		for (int i = 0; i != n + 3; ++i) { //初始化左右
			left[i] = i - 1;
			right[i] = i + 1;
		}
		int op, x, y, chan(0);
		while (m--) {
			scanf("%d", &op);
			if (op == 4) chan = !chan;
			else {
				scanf("%d%d", &x, &y);
				if (chan && (op == 1 || op == 2)) {
					if (op == 1) op = 2;
					else op = 1;
				}
				if (op == 1) {
					left[right[x]] = left[x];
					right[left[x]] = right[x];
					left[x] = left[y];
					right[x] = y;
					right[left[y]] = x;
					left[y] = x;
				}else if (op == 2) {
					left[right[x]] = left[x];
					right[left[x]] = right[x];
					right[x] = right[y];
					left[x] = y;
					left[right[y]] = x;
					right[y] = x;
				}else {
					int lx = left[x], ly = left[y], 
						rx = right[x], ry = right[y];
					if (rx == y) {
						left[y] = lx;
						right[x] = ry;
						right[y] = left[ry] = x;
						left[x] = right[lx] = y;
					} else if (lx == y) {
						left[x] = ly;
						right[y] = rx;
						right[x] = left[rx] = y;
						left[y] = right[ly] = x;
					} else {
						right[lx] = left[rx] = y;
						right[ly] = left[ry] = x;
						left[x] = ly;
						right[x] = ry;
						left[y] = lx;
						right[y] = rx;
					}
				}
			}
		}
		long long sum(0);
		int b(0);
		if (chan) {
			b = n + 1;
			for (int i = 1; i != n + 1; ++i) {
				b = left[b];
				if (i % 2) sum += b;
		//	printf("%d ", b); //*
			}
		} else {
			for (int i = 1; i != n + 1; ++i) {
				b = right[b];
				if (i % 2) sum += b;
	//			printf("%d ", b); //*
			}
		}
		printf("Case %d: %lld\n", ++times, sum);
	}
	return 0; 
}