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Update Longest Increasing Subsequence (nlogn).cpp

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John Law 2019-10-08 23:58:49 +08:00 committed by GitHub
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1 changed files with 36 additions and 29 deletions
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Dynamic Programming/Longest Increasing Subsequence (nlogn).cpp
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@ -3,18 +3,25 @@
// tested on : https://cses.fi/problemset/task/1145/ // tested on : https://cses.fi/problemset/task/1145/
#include <bits/stdc++.h> #include <bits/stdc++.h>
using namespace std; using namespace std;
int LIS(int arr[], int n) int LIS(int arr[], int n)
{ {
set < int > active; // The current built LIS. set < int > active; // The current built LIS.
active.insert(arr[0]); active.insert(arr[0]);
// Loop through every element. // Loop through every element.
for(int i=1; i<n; ++i){ for (int i = 1; i < n; ++i)
{
auto get = active.lower_bound(arr[i]); auto get = active.lower_bound(arr[i]);
if( get == active.end() ){ active.insert(arr[i]); } // current element is the greatest so LIS increases by 1. if (get == active.end())
else{ {
active.insert(arr[i]);
} // current element is the greatest so LIS increases by 1.
else
{
int val = * get; // we find the position where arr[i] will be in the LIS. If it is in the LIS already we do nothing int val = * get; // we find the position where arr[i] will be in the LIS. If it is in the LIS already we do nothing
if( val > arr[i] ){ if (val > arr[i])
{
// else we remove the bigger element and add a smaller element (which is arr[i]) and continue; // else we remove the bigger element and add a smaller element (which is arr[i]) and continue;
active.erase(get); active.erase(get);
active.insert(arr[i]); active.insert(arr[i]);