HDU 3586 Information Disturbing 树形DP

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代码1：

#include<stdio.h>#include<string.h>#include<algorithm>using namespace std;#define maxn 1003#define inf 1<<29struct node{    int v, next, w;}edge[maxn<<1];int n, m;int head[maxn];int tot;void init(){    tot = 0;    memset(head, -1, sizeof(head));}void add(int x, int y, int w){    edge[tot].v = y;    edge[tot].w = w;    edge[tot].next = head[x];    head[x] = tot++;}int minz(int a, int b){    return a < b ? a : b;}int dp[1003];void dfs(int u, int pre, int sum){    int i;    bool flag = 0;    int tmp = 0;    for(i = head[u]; i != -1; i = edge[i].next)    {        int v = edge[i].v;        int w = edge[i].w;        if(v == pre) continue;        dfs(v, u, sum);            flag = 1;        if(w <= sum) tmp += minz(dp[v], w);        else         {            if(dp[v] < inf)                tmp += dp[v];            else flag = 0;        }        if(!flag) break;    }    if(flag) dp[u] = minz(dp[u], tmp);}int main(){    int i, j;    int x, y, w;    while( ~scanf("%d%d", &n, &m) && (n||m) )    {        init();        for(i = 0; i < n-1; i++)        {            scanf("%d%d%d", &x, &y, &w);            add(x, y, w);            add(y, x, w);        }        int l = 0, r = m;        while(l <= r)        {            int mid = (l + r) >> 1;            for(i = 1; i <= n; i++)                dp[i] = inf;            dfs(1, 1, mid);            if(dp[1] > m) l = mid + 1;            else r = mid - 1;            //printf("l = %d r = %d\n", l, r);        }        if(l > m) puts("-1");        else printf("%d\n", l);    }    return 0;}

代码2：

#include<stdio.h>#include<string.h>#include<algorithm>using namespace std;#define maxn 1003#define inf 1000001 //注意别太大，不然会超intstruct node{    int v, next, w;}edge[maxn<<1];int head[maxn];int tot;int n, m;void init(){    tot = 0;    memset(head, -1, sizeof(head));}void add(int x, int y, int w){    edge[tot].v = y;    edge[tot].w = w;    edge[tot].next = head[x];    head[x] = tot++;}int minz(int a, int b){    return a < b ? a : b;}int dp[1003];void dfs(int u, int pre, int sum){    int i;    bool flag = 0;    int tmp = 0;    for(i = head[u]; i != -1; i = edge[i].next)    {        int v = edge[i].v;        int w = edge[i].w;        if(v == pre) continue;        //printf("v = %d w = %d\n", v, w);        dfs(v, u, sum);        if(w <= sum) tmp += minz(dp[v], w);        else tmp += dp[v];        flag = 1;    }    if(flag) dp[u] = minz(dp[u], tmp);}int main(){    int i, j;    int x, y, w;    while( ~scanf("%d%d", &n, &m) && (n||m) )    {        init();        for(i = 0; i < n-1; i++)        {            scanf("%d%d%d", &x, &y, &w);            add(x, y, w);            add(y, x, w);        }        int l = 0, r = m;        while(l <= r)        {            int mid = (l + r) >> 1;            for(i = 1; i <= n; i++)                dp[i] = inf;            dfs(1, 1, mid);            if(dp[1] > m) l = mid + 1;            else r = mid - 1;            //printf("l = %d r = %d\n", l, r);        }        if(l > m) puts("-1");        else printf("%d\n", l);    }    return 0;}