HDU 2196 Computer 树形DP(2个dfs)

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树形DP， 2 个dfs。
前几天觉得很难，现在可以说是水题了。
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#include<stdio.h>#include<string.h>#include<algorithm>using namespace std;#define maxn 10003struct E{    int v, next, w;}edge[maxn<<1];int tot, head[maxn];int n, m;void init(){    tot = 0;    memset(head, -1, sizeof(int)*(n+1));}void add(int s, int t, int w){    edge[tot].v = t;    edge[tot].w = w;    edge[tot].next = head[s];    head[s] = tot++;}int f1[maxn], f2[maxn];int g1[maxn], g2[maxn];void dfs1(int u, int pre){    int i;    f1[u] = f2[u] = 0;    for(i = head[u]; i != -1; i = edge[i].next)    {        int v = edge[i].v;        if(v == pre) continue;        int w = edge[i].w;        dfs1(v, u);        if(f1[v] + w > f2[u])        {            f2[u] = f1[v] + w;            g2[u] = v;            if(f1[u] < f2[u])            {                swap(f1[u], f2[u]);                swap(g1[u], g2[u]);            }        }    }}void dfs2(int u, int pre){    int i;    for(i = head[u]; i != -1; i = edge[i].next)    {        int v = edge[i].v;        if(v == pre) continue;        int w = edge[i].w;        if(g1[u] == v)        {            if(f2[v] < f2[u] + w)            {                f2[v] = f2[u] + w;                g2[v] = u;                if(f1[v] < f2[v])                {                    swap(f1[v], f2[v]);                    swap(g1[v], g2[v]);                }            }        }        else        {            if(f2[v] < f1[u] + w)            {                f2[v] = f1[u] + w;                g2[v] = u;                if(f1[v] < f2[v])                {                    swap(f1[v], f2[v]);                    swap(g1[v], g2[v]);                }            }        }        dfs2(v, u);    }}int main(){    int i, j;    int x, y;    while( ~scanf("%d", &n))    {        init();        for(i = 2; i <= n; i++)        {            scanf("%d%d", &x, &y);            add(i, x, y);            add(x, i, y);        }        dfs1(1, -1);        dfs2(1, -1);        for(i = 1; i <= n; i++)            printf("%d\n", f1[i]);    }    return 0;}