POJ 3321 Apple Tree DFS序 + 樹狀數組

標籤：

多次修改一棵樹節點的值，或者詢問當前這個節點的子樹所有節點權值總和。

首先預先處理出DFS序L[i]和R[i]

把問題轉化為區間查詢總和問題。單點修改，區間查詢，樹狀數組即可。

注意修改的時候也要按照dfs序修改，因為你查詢就是按照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];//樹狀數組，多case的記得要清空int lowbit (int x)//得到x二進位末尾0的個數的2次方 2^num{    return x&(-x);}void addc (int pos,int val)//在第pos位加上val這個值{    while (pos<=n) { //n是元素的個數        c[pos] += val;        pos += lowbit(pos);    }    return ;}int get_sum (int pos) //求解：1--pos的總和{    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]; //查詢用dfs序查，那麼更改也要用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;}

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POJ 3321 Apple Tree DFS序 + 樹狀數組