HDU 4046 - Panda (线段树 + 单点更新)

题意

给出一个字符串，有两种操作。一种是询问[l, r]里有几个wbw，还有是修改某个点的字符。

思路

可以用一个点表示这个点的前三个是不是组成wbw，是就1，不是0.这样就可以通过线段树来处理。

如果修改了一个点，就要修改另外被影响的两个点。

代码

  
  
  
  

   
   
   
   
#include <cstdio>
   
   
   
   
#include <stack>
   
   
   
   
#include <set>
   
   
   
   
#include <iostream>
   
   
   
   
#include <string>
   
   
   
   
#include <vector>
   
   
   
   
#include <queue>
   
   
   
   
#include <functional>
   
   
   
   
#include <cstring>
   
   
   
   
#include <algorithm>
   
   
   
   
#include <cctype>
   
   
   
   
#include <string>
   
   
   
   
#include <map>
   
   
   
   
#include <cmath>
   
   
   
   
#define LL long long
   
   
   
   
#define SZ(x) (int)x.size()
   
   
   
   
#define Lowbit(x) ((x) & (-x))
   
   
   
   
#define MP(a, b) make_pair(a, b)
   
   
   
   
#define MS(arr, num) memset(arr, num, sizeof(arr))
   
   
   
   
#define PB push_back
   
   
   
   
#define F first
   
   
   
   
#define S second
   
   
   
   
#define ROP freopen("input.txt", "r", stdin);
   
   
   
   
#define MID(a, b) (a + ((b - a) >> 1))
   
   
   
   
#define LC rt << 1, l, mid
   
   
   
   
#define RC rt << 1|1, mid + 1, r
   
   
   
   
#define LRT rt << 1
   
   
   
   
#define RRT rt << 1|1
   
   
   
   
#define BitCount(x) __builtin_popcount(x)
   
   
   
   
const double PI = acos(-1.0);
   
   
   
   
const int INF = 0x3f3f3f3f;
   
   
   
   
using namespace std;
   
   
   
   
const int MAXN = 5e4 + 10;
   
   
   
   
const int MOD = 100000007;
   
   
   
   

   
   
   
   
typedef pair<int, int> pii;
   
   
   
   
typedef vector<int>::iterator viti;
   
   
   
   
typedef vector<pii>::iterator vitii;
   
   
   
   

   
   
   
   
int vmax[MAXN << 2];
   
   
   
   

   
   
   
   
char str[MAXN];
   
   
   
   

   
   
   
   
void PushUp(int rt)
   
   
   
   
{
   
   
   
   
 vmax[rt] = vmax[LRT] + vmax[RRT];
   
   
   
   
}
   
   
   
   

   
   
   
   
void Build(int rt, int l, int r)
   
   
   
   
{
   
   
   
   
 if (l == r)
   
   
   
   
 {
   
   
   
   
 if (l >= 3)
   
   
   
   
 if (str[l] == 'w' && str[l - 1] == 'b' && str[l - 2] == 'w') vmax[rt] = 1;
   
   
   
   
 else vmax[rt] = 0;
   
   
   
   
 else vmax[rt] = 0;
   
   
   
   
 return;
   
   
   
   
 }
   
   
   
   
 int mid = MID(l, r);
   
   
   
   
 Build(LC); Build(RC);
   
   
   
   
 PushUp(rt);
   
   
   
   
}
   
   
   
   

   
   
   
   
void Update(int rt, int l, int r, int pos)
   
   
   
   
{
   
   
   
   
 if (l == r)
   
   
   
   
 {
   
   
   
   
 if (str[l] == 'w' && str[l - 1] == 'b' && str[l - 2] == 'w') vmax[rt] = 1;
   
   
   
   
 else vmax[rt] = 0;
   
   
   
   
 return;
   
   
   
   
 }
   
   
   
   
 int mid = MID(l, r);
   
   
   
   
 if (pos <= mid) Update(LC, pos);
   
   
   
   
 else Update(RC, pos);
   
   
   
   
 PushUp(rt);
   
   
   
   
}
   
   
   
   

   
   
   
   
int Query(int rt, int l, int r, int L, int R)
   
   
   
   
{
   
   
   
   
 if (L <= l && r <= R) return vmax[rt];
   
   
   
   
 int mid = MID(l, r), ans = 0;
   
   
   
   
 if (L <= mid) ans += Query(LC, L, R);
   
   
   
   
 if (R > mid) ans += Query(RC, L, R);
   
   
   
   
 return ans;
   
   
   
   
}
   
   
   
   

   
   
   
   
int main()
   
   
   
   
{
   
   
   
   
 //ROP;
   
   
   
   
 int T, i, j, cases = 0;
   
   
   
   
 scanf("%d", &T);
   
   
   
   
 while (T--)
   
   
   
   
 {
   
   
   
   
 printf("Case %d:\n", ++cases);
   
   
   
   
 int m, n;
   
   
   
   
 scanf("%d%d", &m, &n);
   
   
   
   
 scanf("%s", str + 1);
   
   
   
   
 Build(1, 1, m);
   
   
   
   
 while (n--)
   
   
   
   
 {
   
   
   
   
 int a, b;
   
   
   
   
 scanf("%d%d%*c", &a, &b);
   
   
   
   
 if (a == 0)
   
   
   
   
 {
   
   
   
   
 int c;
   
   
   
   
 scanf("%d", &c);
   
   
   
   
 if (c - b < 2)
   
   
   
   
 {
   
   
   
   
 puts("0");
   
   
   
   
 continue;
   
   
   
   
 }
   
   
   
   
 printf("%d\n", Query(1, 1, m, b + 3, c + 1));
   
   
   
   
 }
   
   
   
   
 else
   
   
   
   
 {
   
   
   
   
 b++;
   
   
   
   
 char c;
   
   
   
   
 scanf("%c", &c);
   
   
   
   
 str[b] = c;
   
   
   
   
 if (b >= 3) Update(1, 1, m, b);
   
   
   
   
 if (b >= 2 && b + 1 <= m) Update(1, 1, m, b + 1);
   
   
   
   
 if (b >= 1 && b + 2 <= m) Update(1, 1, m, b + 2);
   
   
   
   
 }
   
   
   
   

   
   
   
   
 }
   
   
   
   
 }
   
   
   
   
 return 0;
   
   
   
   
}