题目大意：有一个长度为$n$的$01$串，两个操作：
- $1\;l\;r：$把区间$[l,r]$翻转（$0->1,1->0$）
- $2\;p：$求第$p$位是什么
题解：维护前缀异或和，树状数组即可
卡点：无
C++ Code：
#include#include namespace std { struct istream {#define M (1 << 24 | 3) char buf[M], *ch = buf - 1; inline istream() {#ifndef ONLINE_JUDGE freopen("input.txt", "r", stdin);#endif fread(buf, 1, M, stdin); } inline istream& operator >> (int &x) { while (isspace(*++ch)); for (x = *ch & 15; isdigit(*++ch); ) x = x * 10 + (*ch & 15); return *this; }#undef M } cin; struct ostream {#define M (1 << 24 | 3) char buf[M], *ch = buf - 1; int w; inline ostream& operator << (int x) { if (!x) { *++ch = '0'; return *this; } for (w = 1; w <= x; w *= 10); for (w /= 10; w; w /= 10) *++ch = (x / w) ^ 48, x %= w; return *this; } inline ostream& operator << (const char x) {*++ch = x; return *this;} inline ostream& operator << (const char *x) { while (*x) *this << *x++; return *this; } inline ~ostream() {#ifndef ONLINE_JUDGE freopen("output.txt", "w", stdout);#endif fwrite(buf, 1, ch - buf + 1, stdout); }#undef M } cout;}#define maxn 100010int n, m;namespace BIT { int Tr[maxn], res; inline void add(int p) {for (; p <= n; p += p & -p) Tr[p] ^= 1;} inline int ask(int p) {for (res = 0; p; p &= p - 1) res ^= Tr[p]; return res;}}int main() { std::cin >> n >> m; while (m --> 0) { int op, l, r; std::cin >> op >> l; if (op == 1) { std::cin >> r; BIT::add(l), BIT::add(r + 1); } else std::cout << BIT::ask(l) << '\n'; } return 0;}