poj3250

利用栈进行动态规划，要注意的地方是总和得用longlong因为80000^2是超出int范围的。

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      #include 
    
      <
    
      cstdio
    
      >
    
      
#include 
    
      <
    
      iostream
    
      >
    
      
#include 
    
      <
    
      cstdlib
    
      >
    
      
#include 
    
      <
    
      cstring
    
      >
    
      

    
      using
    
       
    
      namespace
    
       std;


    
      #define
    
       maxn 80002
    
      


    
      struct
    
       item
{
 
    
      int
    
       num, h;
}stk[maxn];


    
      int
    
       cow[maxn], f[maxn], front 
    
      =
    
       
    
      0
    
      ;


    
      int
    
       main()
{
 
    
      //
    
      freopen("D:\\t.txt", "r", stdin);
    
      

    
       
    
      int
    
       n;
 scanf(
    
      "
    
      %d
    
      "
    
      , 
    
      &
    
      n);
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       n; i
    
      ++
    
      )
 scanf(
    
      "
    
      %d
    
      "
    
      , 
    
      &
    
      cow[i]);
 stk[front].num 
    
      =
    
       n 
    
      -
    
       
    
      1
    
      ;
 stk[front
    
      ++
    
      ].h 
    
      =
    
       cow[n 
    
      -
    
       
    
      1
    
      ];
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       n 
    
      -
    
       
    
      2
    
      ; i 
    
      >=
    
       
    
      0
    
      ; i
    
      --
    
      )
 {
 
    
      while
    
       (cow[i] 
    
      >
    
       stk[front 
    
      -
    
       
    
      1
    
      ]. h 
    
      &&
    
       front 
    
      >
    
       
    
      0
    
      )
 front
    
      --
    
      ;
 
    
      if
    
       (front 
    
      ==
    
       
    
      0
    
      )
 {
 f[i] 
    
      =
    
       n 
    
      -
    
       i 
    
      -
    
       
    
      1
    
      ;
 stk[front].num 
    
      =
    
       i;
 stk[front
    
      ++
    
      ].h 
    
      =
    
       cow[i];
 
    
      continue
    
      ;
 }
 f[i] 
    
      =
    
       stk[front 
    
      -
    
       
    
      1
    
      ]. num 
    
      -
    
       i 
    
      -
    
       
    
      1
    
      ;
 stk[front].num 
    
      =
    
       i;
 stk[front
    
      ++
    
      ].h 
    
      =
    
       cow[i];
 }
 
    
      long
    
       
    
      long
    
       sum 
    
      =
    
       
    
      0
    
      ;
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       n; i
    
      ++
    
      )
 sum 
    
      +=
    
       f[i];
 printf(
    
      "
    
      %I64d\n
    
      "
    
      , sum);
 
    
      return
    
       
    
      0
    
      ;
}