HDU

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3572

#include<bits/stdc++.h>

using namespace std;
typedef long long ll;
const int maxn = 1e5 + 10;
const int inf = 0x3f3f3f3f;

int head[maxn * 2], depth[maxn * 2], cur[maxn * 2];
int ans, t, n, m, s, x, y, z, mx, k, sum, q, cnt = 1;

struct st
{
    int to, next, w;
}e[maxn * 2];

inline void add(int u, int v, int w)
{
    e[++cnt].to = v;
    e[cnt].next = head[u];
    e[cnt].w = w;
    head[u] = cnt;
}

inline int dfs(int u, int flow)
{
    if(u == t) return flow;
    int ret = 0;
    for(int &i = cur[u]; i; i = e[i].next) // 弧优化
    {
        int v = e[i].to;
        if(depth[v] == depth[u] + 1 && e[i].w)
        {
            int di = dfs(v, min(e[i].w, flow - ret)); // 多路增广优化
            ret += di; e[i].w -= di; e[i ^ 1].w += di;
            if(flow - ret == 0) break;
        }
        
    }
    
    if(!ret) depth[u] = -1; // 炸点优化
    return ret;
}

int bfs() // 分层
{
    queue<int> q;
    q.push(s);
    memset(depth, 0, sizeof(depth));
    depth[s] = 1;
    
    while(!q.empty())
    {
        int u = q.front(); q.pop();
        for(int i = head[u]; i; i = e[i].next)
        {
            int v = e[i].to;
            if(!depth[v] && e[i].w)
            {
                depth[v] = depth[u] + 1;
                q.push(v);
            }
            
        }
        
    }
    
    return depth[t];
}

int dinic()
{
    int ans = 0;
    while(bfs())
    {
        for(int i = 0; i <= cnt; ++i) cur[i] = head[i];
        ans += dfs(s, inf);
    }
    
    return ans;
}

int main()
{
    scanf("%d", &q);
    while(q--)
    {
        k++;
        scanf("%d %d", &n, &m);
        memset(e, 0, sizeof(e));
        memset(head, 0, sizeof(head));
        
        cnt = 1;
        s = 0; mx = -inf; sum = 0;
        
        for(int i = 1; i <= n; ++i)
        {
            scanf("%d %d %d", &x, &y, &z);
            sum += x;
            add(s, i, x), add(i, s, 0);
            for(int j = y; j <= z; ++j)
            {
                add(i, j + n, 1), add(j + n, i, 0);
                mx = max(mx, z);
            }
            
        }
        
        t = mx + 1;
        for(int i = 1; i <= mx; ++i)
        {
            add(i + n, t, m), add(t, i + n, 0);
        }
        
        ans = dinic();
        if(ans == sum) printf("Case %d: Yes
", k);
        else printf("Case %d: No
", k);
        
        cout<<endl;
    }
    
    return 0;
}

for(int &i = cur[u]; i; i = e[i].next)
    {

和

for(int i = cur[u]; i; i = e[i].next)
   {

        cur[u] = i;

效果是一样的，去掉&也不能说错因为cur本来和head就是一样的，去掉就失去了优化的效果了