"Reprint" "Tree array interval k big/small"

Original posts: http://www.cnblogs.com/zgmf_x20a/archive/2008/11/15/1334109.html

Recalling the definition of a tree array, note the following two properties:
One, c[ans]=sum of a[ans-lowbit (ans) +1 ... ans];
Second, when Ans=2^k,
C[ans]=sum of a[1 ... ans];

The following shows how Findk (k) Works:
1, set the boundary condition Ans,ans ' <maxn and cnt<=k;
2, initialize Cnt=c[ans], where ans=2^k and K are the largest integers that satisfy the boundary conditions;
3. Find the largest ans ' that satisfies the boundary conditions ' so that ans '-lowbit (ans ') =ans, i.e. ans ' satisfies c[ans ']=a[ans+1. Ans '] (according to the nature of one), as long as the C[ans '] is added to CNT (at this time cnt=sum of a[ 1 ... ans '], according to the nature of the second), CNT can be used as the approximate value of k;
4, repeat the 3rd step until CNT can no longer approximate k, when ans is just 1 smaller than the solution, return to ans+1.

So the essence of FINDK (k) is the approximation of two points

1 /**********************************2 3 tree-like array to find elements of K-small4 5 Classic. 6 7 limit: Data range within 1<<208 9 ***********************************/Ten  One#include <iostream> A  - using namespacestd; -  the  -  - #defineMAXN 1<<20 -  + intn,k; -  + intC[MAXN]; A  at  -  - intLowbit (intx) { -  -     returnx&-x; -  in } -  to  +  - voidInsertintXintt) { the  *         while(x<MAXN) { $ Panax Notoginsengc[x]+=T; -  thex+=lowbit (x);  +  A        } the  + } -  $ intFindintk) { $  -     intCnt=0, ans=0; -  the      for(intI= -; i>=0; i--){ - Wuyians+= (1<<i); the  -         if(ANS&GT;=MAXN | | cnt+c[ans]>=k) ans-= (1<<i); Wu  -         Elsecnt+=C[ans]; About  $     } -  -     returnans+1; -  A } +  the voidinput () { -  $Memset (c,0,sizeof(c)); the  the        intT; the  thescanf"%d%d",&n,&k); -  in         for(intI=0; i<n;i++){     the  thescanf"%d",&t); About  theInsert (T,1); the  the        } +  -printf"%d\n", find (k)); the Bayi } the  the intMain () { -  -     intcases; the  thescanf"%d",&cases); the  the      while(cases--){ -  the input (); the  the     }94  the     return 0; the  the}

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"Reprint" "Tree array interval k big/small"