题解 [ABC155F] Perils in Parallel

include <bits/stdc++.h>

define N 200005

using namespace std;

int n, m;
int head[N], nex[N << 1], to[N << 1], eid[N << 1], ecnt;
int p[N], s[N];

struct light {
int pos, state;
}lig[N];

bool cmpLight(const light &lhs, const light &rhs) { return lhs.pos < rhs.pos; }

inline int read() {
int x = 0; char ch = getchar();
while(!isdigit(ch)) ch = getchar();
while(isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
return x;
}
inline void addE(int u, int v, int id) {
to[++ecnt] = v, eid[ecnt] = id;
nex[ecnt] = head[u], head[u] = ecnt;
}

int cntOne;
int dif[N], fa[N], fe[N];
bool vis[N];

void dfs(int u) {
if(s[u]) ++dif[u], ++cntOne;
for(int i = head[u], v; i; i = nex[i]) {
v = to[i];
if(fa[v]) continue;
fa[v] = u, fe[v] = eid[i], dfs(v);
dif[u] += dif[v];
}
}

int main() {
n = read(), m = read();
for(int i = 1; i <= n; ++i)
lig[i].pos = read(), lig[i].state = read();

sort(lig + 1, lig + n + 1, cmpLight);
for(int i = 1; i <= n; ++i)
	p[i] = lig[i].pos, s[i] = lig[i].state;
for(int i = n + 1; i >= 1; --i)
	s[i] = s[i] ^ s[i - 1];
	
for(int i = 1, l, r; i <= m; ++i) {
	l = read(), r = read();
	l = lower_bound(p + 1, p + n + 1, l) - p;
	r = upper_bound(p + 1, p + n + 1, r) - p - 1;
	if(l <= r) {
		addE(l, r + 1, i), addE(r + 1, l, i);
	}
}

for(int i = 1; i <= n + 1; ++i)
	if(!fa[i]) {
		fa[i] = i;
		dfs(i);
		if(cntOne & 1) {
			puts("-1");
			return 0;
		}
	}

int cnt = 0;
for(int i = 1; i <= n + 1; ++i)
	if(dif[i] & 1)
		vis[fe[i]] = true, ++cnt;

printf("%d\n", cnt);
for(int i = 1; i <= m; ++i)
	if(vis[i])
		printf("%d ", i);
putchar('\n');
return 0;

}