hdu 4274 Spy’s Work DFS 貪心

題意：一個結構像一棵樹一樣的公司。一個間諜去打探，然後發回來一些訊息，讓我們判斷真假。

做法：這些訊息裡只要有一條不對，這個間諜就在撒謊。 不對的情況是最終的上界小於下界，或者結合資訊做出來的某個節點不合理。

#include <cstdio>#include <cstring>#define max(a, b) ((a) > (b) ? (a) : (b))#define min(a, b) ((a) < (b) ? (a) : (b))typedef __int64 LL;#define inf 1e15; const int LMT = 10002;LL __up[LMT], __down[LMT], ori_down[LMT];int next[LMT], all;struct __line{    int u, v, next;}e[LMT << 1];void init(void){    memset(next, -1, sizeof(next));    memset(ori_down, 0, sizeof(ori_down));    for(int i = 0; i < LMT; ++i)    {        __up[i] = inf;        __down[i] = 1;    }    all = 0;}void insert(int u, int v){    e[all].u = u;    e[all].v = v;    e[all].next =  next[u];    next[u] = all++;}void dfs(int u, int pre){    int v, x;    for(x = next[u]; x != -1; x = e[x].next)    if(e[x].v != pre)    {        v = e[x].v;        dfs(v, u);        ori_down[u] += max(ori_down[v], __down[v]);     }    ++ori_down[u];}int main(void){    int n, i , j, m;    char tag;    while(~scanf("%d", &n))    {        init();        for(j = 2; j <= n; ++j)        {            scanf("%d", &i);            insert(i, j);            insert(j, i);        }        scanf("%d", &m);        while(m--)        {            scanf("%d %c %d", &i, &tag, &j);            switch(tag)            {            case '>':__down[i] = max(__down[i], j + 1); break;            case '<':__up[i] = min(__up[i], j - 1); break;            case '=':    __down[i] = max(__down[i], j);                         __up[i] = min(__up[i], j);                     break;            }        }        dfs(1, -1);        for(i = 1; i <= n; ++i)            if(__up[i] < __down[i] || ori_down[i] > __up[i])            {                printf("Lie\n");                break;            }       if(i > n)printf("True\n");    }    return 0;}