Create suffix_array.cpp

String_Algo/suffix_array.cpp

@@ -0,0 +1,126 @@
+#include<bits/stdc++.h>
+using namespace std;
+typedef long long int ll;
+typedef unsigned long long int ull;
+typedef long double ld;
+#define MOD 1000000007
+#define INF 1000000000000000000
+#define endll "\n"
+#define pb push_back
+#define forn(i,n) for(i=0;i<n;i++)
+#define forab(i,a,b) for(i=a;i<=b;i++)
+#define vpll vector<pair<ll,ll>>
+#define pll pair<ll,ll>
+#define vll vector<ll>
+#define ff first
+#define ss second
+#define bs binary_search
+#define lb lower_bound
+#define ub upper_bound
+#define test ll t;cin>>t; while(t--)
+#define fast_io ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
+
+ vll SortCharacters(string& s)
+ {
+  vll order(s.length());
+  ll count[27]={0},i;
+  for(i=0;i<s.length()-1;i++)
+  {
+    count[s[i]-'A'+1]++;
+  }
+  count[0]++;
+  for(i=1;i<27;i++)
+  {
+    count[i]=count[i]+count[i-1];
+  }
+
+  order[0]=s.length()-1;
+  for(i=s.length()-2;i>=0;i--)
+  {
+    ll x=s[i]-'A'+1;
+    count[x]-=1;
+    order[count[x]]=i;
+  }
+  return order;
+ }
+
+ vll ComputeCharClasses(string& s, vll& order)
+ {
+  vll clss(s.length());
+  ll i;
+  clss[order[0]]=0;
+  for(i=1;i<s.length();i++)
+  {
+    if(s[order[i]]!=s[order[i-1]])
+      clss[order[i]]=clss[order[i-1]]+1;
+    else
+      clss[order[i]]=clss[order[i-1]];
+  }
+  return clss;
+ }
+
+ vll SortDoubled(string& s,ll len,vll& order,vll& clss)
+ {
+  ll count[s.length()]={0};
+  ll i,start,cl;
+  vll newOrder(s.length());
+  for(i=0;i<s.length();i++)
+  {
+    count[clss[i]]++;
+  }
+  for(i=1;i<s.length();i++)
+  {
+    count[i]=count[i]+count[i-1];
+  }
+  for(i=s.length()-1;i>=0;i--)
+  {
+    start=(order[i]-len+s.length())%s.length();
+    cl=clss[start];
+    count[cl]-=1;
+    newOrder[count[cl]]=start;
+  }
+  return newOrder;
+ }
+
+ vll UpdateClasses(vll& newOrder,vll& clss,ll len)
+ {
+  ll n=newOrder.size(),i,cur,prev,midprev,mid;
+  vll newClass(n);
+  newClass[newOrder[0]]=0;
+  for(i=1;i<n;i++)
+  {
+    cur=newOrder[i];
+    prev=newOrder[i-1];
+    mid=(cur+len)%n;
+    midprev=(prev+len)%n;
+    if(clss[cur]!=clss[prev] || clss[mid]!=clss[midprev])
+      newClass[cur]=newClass[prev]+1;
+    else
+      newClass[cur]=newClass[prev];
+  }
+  return newClass;
+ }
+
+int main()
+{
+  fast_io;
+  string s;
+  cin>>s;
+  ll i;
+  vll order=SortCharacters(s);
+  vll clss=ComputeCharClasses(s,order);
+  ll len=1;
+  while(len<s.length())
+  {
+    order=SortDoubled(s,len,order,clss);
+    clss=UpdateClasses(order,clss,len);
+    len=2*len;
+  }
+  for(i=0;i<s.length();i++)
+    cout<<order[i]<<" ";
+  cout<<endl;
+  return 0;
+}
+
+/* Example: AAA$
+   Output: 3 2 1 0 */