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POJ 3321 Apple Tree DFS序 + 树状数组
多次修改一棵树节点的值,或者询问当前这个节点的子树所有节点权值总和。
首先预处理出DFS序L[i]和R[i]
把问题转化为区间查询总和问题。单点修改,区间查询,树状数组即可。
注意修改的时候也要按照dfs序修改,因为你查询就是按照dfs查的,所以修改也要用dfs序修改
L[i]是唯一的。
#include <cstdio>#include <cstdlib>#include <cstring>#include <cmath>#include <algorithm>using namespace std;#define inf (0x3f3f3f3f)typedef long long int LL;#include <iostream>#include <sstream>#include <vector>#include <set>#include <map>#include <queue>#include <string>const int maxn = 100000 + 20;int first[maxn], L[maxn], R[maxn], a[maxn];struct edge { int u, v; int next;} e[maxn * 2];int n, num;void add (int u, int v){ ++num; e[num].u = u; e[num].v = v; e[num].next = first[u]; first[u] = num;}bool book[maxn];int index;void dfs (int cur){ L[cur] = index; for (int i = first[cur]; i; i = e[i].next) { if (book[e[i].v] == 0) { book[e[i].v] = 1; index++; dfs (e[i].v); } } R[cur] = index;}int c[maxn];//树状数组,多case的记得要清空int lowbit (int x)//得到x二进制末尾0的个数的2次方 2^num{ return x&(-x);}void addc (int pos,int val)//在第pos位加上val这个值{ while (pos<=n) { //n是元素的个数 c[pos] += val; pos += lowbit(pos); } return ;}int get_sum (int pos) //求解:1--pos的总和{ int ans = 0; while (pos) { ans += c[pos]; pos -= lowbit(pos); } return ans;}void work (){ for (int i = 1; i <= n - 1; ++i) { int u, v; scanf ("%d%d", &u, &v); add (u, v); } for (int i = 1; i <= n; ++i) { addc (i, 1); a[i] = 1; } dfs (1); int m; scanf ("%d", &m); for (int i = 1; i <= m; ++i) { char str[3]; int id; scanf ("%s%d", str, &id); if (str[0] == ‘Q‘) { printf ("%d\n", get_sum (R[id]) - get_sum (L[id] - 1)); } else { id = L[id]; //查询用dfs序查,那么更改也要用dfs序更改 a[id] = -a[id]; addc (id, a[id]); } } return ;}int main (){#ifdef local freopen("data.txt","r",stdin);#endif while (~scanf ("%d", &n)) { index = 1; work (); memset (first, 0, sizeof first); num = 0; memset (book, 0, sizeof book); memset (c, 0, sizeof c); } return 0;}
POJ 3321 Apple Tree DFS序 + 树状数组
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