LashaBukhnikashvili's blog

SPOJ K-th Number
By LashaBukhnikashvili, 10 years ago, In English

here is the link of a problem,I wrote O(n log n + m log^3 n) solution,but I have wa16, here is my code.

please help to find my mistake,also I am interested log n and log^2 n solutions.

Any help will be appreciated very much :)

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10 years ago, # |
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for O((n+m) log n) solution see here

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    10 years ago, # ^ |
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    could you explain your solution?

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      10 years ago, # ^ |
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      Sort the array keeping track of indexes so I have A[0] is the index of smallest number and A[n-1] is the index of biggest number

      Now if I want K-th smallest number in range [l,r] the naive way is like the code 

      int tmp=0;
for(int i=0;i<n;i++){
if(l<=A[i] && A[i]<=r)tmp++;
if(tmp==k){
cout<<A[i]<<endl; //output the index
break;
}
}

      This has complexity O(n) for each operation

      I use sqrt decompstion to make it faster

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        10 years ago, # ^ |
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        Can you please comment your code a bit so that it makes it easier to understand? I have no idea what your pre[][] array does and not able to understand it from the link that you've posted.

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          10 years ago, # ^ |
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          pre[i][j] means how many indexes between 1 and j exists in ith block

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        10 years ago, # ^ |
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        it is hard to understand idea from your code, but when you explain I got it,thanks,great idea ;)

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