Added section for string_algorithms

String_algo/KMP.cpp

@@ -0,0 +1,68 @@
+/* 
+   Time-Complexity :- O(length of string)
+   Used for outputing indices where a particular text appears in a given string
+*/
+#include<bits/stdc++.h>
+#include<sstream>
+#include<ext/pb_ds/tree_policy.hpp>
+using namespace std;
+#define mod 1000000007
+#define all(v) v.begin(),v.end()
+#define loop(i,a,b) for(i=(int)a;i<(int)b;i++)
+#define revloop(i,a,b) for(i=(int)a;i>=(int)b;i--)
+#define stloop(it,v) for(it=v.begin();it!=v.end();++it)
+#define ii pair<int,int>
+#define MP make_pair
+#define pb push_back
+#define ll long long int
+#define fill(v,d) memset(v,d,sizeof(v))
+#define INF 1000000005
+#define PI acos(-1.0)
+vector<int> b;
+string p,t;
+int i;
+void preprocess(string a)
+{
+  int i = 1,j = 0;
+  b[0] = 0;
+  while(i < (int)a.length())
+  {
+   while(j > 0 && a[i] != a[j])
+   { j--;
+     j= b[j];
+   }
+   if(a[i] == a[j])
+    j++;
+   b[i] = j;
+   i++;
+  }
+}
+void kmp(string a,string t)
+{
+  int i=0,j=0;
+  while(i<(int)a.length())
+  {
+    while(j > 0 && a[i] != t[j])
+    { j--;
+      j= b[j];
+    }
+    if(a[i] == t[j])
+     j++;
+    if(j == (int)t.length())
+    { cout<<i-j+1<<" ";
+      j=b[t.length()-1];
+    }
+    i++;
+  }
+}
+int main()
+{  std::ios_base::sync_with_stdio(false); cin.tie(NULL);
+   cin>>t>>p;
+   b.resize(p.length());
+   preprocess(p);
+   loop(i,0,b.size())
+    cout<<b[i]<<" ";
+   cout<<endl;
+   kmp(t,p);
+   return 0;
+}

String_algo/SUFFIX-ARRAY.cpp

@@ -0,0 +1,71 @@
+/* 
+   Time-Complexity :- O(nlog(n)^2),where n is the length of string
+   Used for outputing all the suffixes in a sorted way
+*/
+#include<bits/stdc++.h>
+#include<sstream>
+#include<ext/pb_ds/tree_policy.hpp>
+using namespace std;
+#define mod 1000000007
+#define all(v) v.begin(),v.end()
+#define loop(i,a,b) for(i=(int)a;i<(int)b;i++)
+#define revloop(i,a,b) for(i=(int)a;i>=(int)b;i--)
+#define stloop(it,v) for(it=v.begin();it!=v.end();++it)
+#define ii pair<int,string>
+#define MP make_pair
+#define pb push_back
+#define ll long long int
+#define fill(v,d) memset(v,d,sizeof(v))
+#define INF 1000000005
+#define PI acos(-1.0)
+vector<vector<int> > sa;
+struct mytuple{
+ int orig;
+ int first;
+ int second;
+};
+bool cmp(mytuple a,mytuple b)
+{
+  if(a.first == b.first)
+    return a.second < b.second;
+  return a.first < b.first;
+}
+int main()
+{  std::ios_base::sync_with_stdio(false); cin.tie(NULL);
+   string a;
+   int i,n,curr,cnt,stp;
+   cin>>a;
+   n = a.length();
+   stp = log(n)/log(2) + 2;
+   sa.assign(stp,vector<int>(n));
+   loop(i,0,n)
+    sa[0][i] = a[i]-'a';
+   mytuple L[n];
+   stp = 1;
+   for(cnt = 1;cnt < n; cnt*=2)
+   {
+     for(i=0;i<n;i++)
+     {
+      L[i].first = sa[stp-1][i];
+      L[i].orig=i;
+      if(i+cnt<n)
+       L[i].second = sa[stp-1][i+cnt];
+      else
+       L[i].second = -1;
+     }
+     sort(L,L+n,cmp);
+     sa[stp][L[0].orig] = curr = 0;
+     for(i=1;i<n;i++)
+     {
+       if((L[i].first != L[i-1].first) || (L[i].second != L[i-1].second))
+        curr++;
+       sa[stp][L[i].orig] = curr;
+     }
+     stp++;
+   }
+   loop(i,0,n)
+   { stp = L[i].orig;
+     cout<<stp<<" "<<a.substr(stp,n-stp)<<endl;
+   }
+   return 0;
+}

String_algo/z_algorithm.cpp

@@ -0,0 +1,50 @@
+/*
+  Complexity = O(length of string)
+  s = aaabaab => z[] = {-1,2,1,0,2,1,0}
+  s = aaaaa => z[] = {-1,4,3,2,1}
+  s = abacaba => z[] = {-1,0,1,0,3,0,1}
+*/
+#include<bits/stdc++.h>
+using namespace std;
+#define mod 1000000007
+#define all(v) v.begin(),v.end()
+#define rep(i,a,b) for(i=(ll)a;i<(ll)b;i++)
+#define revrep(i,a,b) for(i=(ll)a;i>=(ll)b;i--)
+#define strep(it,v) for(it=v.begin();it!=v.end_();++it)
+#define ii pair<ll,ll>
+#define MP make_pair
+#define pb push_back
+#define f first
+#define se second
+#define ll long long int
+#define vi vector<ll>
+ll modexp(ll a,ll b){ ll res = 1; while(b > 0){  if(b & 1) res = (res * a);  a = (a * a);  b/=2;  }  return res; }
+#define rs resize
+long long readLI(){  register char c;  for(c = getchar(); !(c>='0' && c<='9'); c = getchar());  register long long a=c-'0';
+    for(c = getchar(); c>='0' && c<='9'; c = getchar())
+        a = (a<<3)+(a<<1)+c-'0';
+    return a;
+}
+const int N = 100009;
+string a;
+ll i,z[N];
+void z_function(string s)
+{
+   ll l = 0,r = 0,n = s.length();
+   rep(i,1,n){
+       if(i <= r) z[i] = min(r - i + 1,z[i - l]);
+       while(i + z[i] < n and s[z[i]] == s[i + z[i]])
+        z[i]++;
+       if(i + z[i] - 1 > r)
+         l = i, r = i + z[i] - 1;
+   }
+}
+int main()
+{
+   std::ios_base::sync_with_stdio(false); cin.tie(NULL);
+   cin>>a;
+   z[0] = -1; //Not possible of zero length
+   z_function(a);
+   rep(i,0,a.length()) cout<<z[i]<<" ";
+   return 0;
+}