poj 1040 Transportation

<textarea cols="89" rows="15" name="code" class="cpp">//poj 1040 Transportation (搜索+剪枝) /* 题解：排序，所有order从左到右搜，决定选或不选 PS：一个小小剪枝产生的效果大极了，剪枝前TLE，剪枝后200多MS */ #include &lt;iostream&gt; #include &lt;algorithm&gt; #include &lt;cmath&gt; using namespace std; const int inf = 1&lt;&lt;28; int n,m; int c,ans,mark; struct node { int from,to,num,gain; bool operator &lt; (const node &amp; other) const { if (from==other.from) return to&lt;other.to; return from&lt;other.from; } }ord[22]; void dfs(int step,int sum,int earn,int mark) { if (step&gt;=n) { ans=max(ans,earn); return ; } //以下三行为剪枝 int temp=earn; for (int i=step;i&lt;n;i++) temp+=ord[i].gain; if (temp&lt;ans) return ; for (int i=0;i&lt;step;i++) if ( ((1&lt;&lt;i)&amp;mark) &amp;&amp; ord[i].to&lt;=ord[step].from) sum-=ord[i].num,mark^=(1&lt;&lt;i); dfs(step+1,sum,earn,mark); if (ord[step].num+sum&gt;c) return ; dfs(step+1,sum+ord[step].num,earn+ord[step].gain,mark|(1&lt;&lt;step)); } int main() { while (scanf("%d%d%d",&amp;c,&amp;m,&amp;n) &amp;&amp; c+m+n) { for (int i=0;i&lt;n;i++) { scanf("%d%d%d",&amp;ord[i].from,&amp;ord[i].to,&amp;ord[i].num); ord[i].gain=ord[i].num*(ord[i].to-ord[i].from); } sort(ord,ord+n); ans=mark=0; dfs(0,0,0,0); printf("%d/n",ans); } system("pause"); return 0; } </textarea>