HDU 1540 Tunnel Warfare——特殊查询的线段树

一定要注意查询范围，以及及时变动查询位置，具体参考代码query函数

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <stack>

using namespace std;

const int maxn = 1e5;

stack<int> last;
int n, q;

struct SegTree {
bool is_all0;
int maxL, maxR, max0;
}segTree[maxn<<2];

void pushup(int root) {
segTree[root].is_all0 = segTree[root<<1].is_all0 && segTree[root<<1|1].is_all0;
segTree[root].maxL = segTree[root<<1].maxL + (segTree[root<<1].is_all0 ? segTree[root<<1|1].maxL : 0);
segTree[root].maxR = segTree[root<<1|1].maxR + (segTree[root<<1|1].is_all0 ? segTree[root<<1].maxR : 0);
segTree[root].max0 = max(segTree[root<<1].maxR + segTree[root<<1|1].maxL, max(segTree[root<<1].max0, segTree[root<<1|1].max0));
}

void build(int L, int R, int root) {
if (L == R) {
segTree[root].is_all0 = true;
segTree[root].maxL = segTree[root].maxR = segTree[root].max0 = 1;
return;
}
int mid = (L + R)>>1;
build(L, mid, root<<1);
build(mid + 1, R, root<<1|1);
pushup(root);
}

void update_node(int L, int R, int root, int pos, int val) {
if (L == R) {
segTree[root].is_all0 = val;
segTree[root].maxL = segTree[root].maxR = segTree[root].max0 = val;
return;
}
int mid = (L + R)>>1;
if (pos <= mid) {
update_node(L, mid, root<<1, pos, val);
}
else {
update_node(mid + 1, R, root<<1|1, pos, val);
}
pushup(root);
}

int query(int L, int R, int root, int pos) {
if (L == R || segTree[root].max0 == 0 || segTree[root].max0 == R - L + 1) {
return segTree[root].max0;
}
int mid = (L + R)>>1;
if (pos <= mid) {
if (pos >= mid - segTree[root<<1].maxR + 1) {
return query(L, mid, root<<1, pos) + query(mid + 1, R, root<<1|1, mid + 1);
}
else {
return query(L, mid, root<<1, pos);
}
}
else {
if (pos <= mid + segTree[root<<1|1].maxL) {
return query(mid + 1, R, root<<1|1, pos) + query(L, mid, root<<1, mid);
}
else {
return query(mid + 1, R, root<<1|1, pos);
}
}
}

int main()
{
while (scanf("%d %d", &n, &q) == 2) {
build(1, n, 1);
while (!last.empty()) last.pop();
while (q--) {
char c; cin >> c;
if (c == 'D') {
int x; scanf("%d", &x);
last.push(x);
update_node(1, n, 1, x, 0);
}
else if (c == 'R') {
int x = last.top(); last.pop();
update_node(1, n, 1, x, 1);
}
else {
int x; scanf("%d", &x);
printf("%d\n", query(1, n, 1, x));
}
}
}
return 0;
}