Suffix array of string

Article/README.md

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+# Suffix Array - O(N log N) using the map.
+
+A suffix array is a sorted array of all suffixes of a given string.
+
+For more detail please check:  [Suffix Array | Set 2 (nLogn Algorithm)](https://www.geeksforgeeks.org/suffix-array-set-2-a-nlognlogn-algorithm/#:~:text=A%20suffix%20array%20is%20a,suffixes%20of%20a%20given%20string.&text=We%20have%20discussed%20Naive%20algorithm,while%20sorting%2C%20maintain%20original%20indexes.).
+
+This is a simple way to solve this problem.
+
+```
+ Example:
+
+0     banana                                                             5      a 
+
+1     anana               Sort the Suffixes                              3      ana
+
+2     nana                     ---------------->                         1      anana  
+
+3     ana                    alphabetically                              0       banana  
+
+4     na                                                                 4       na  
+
+5     a                                                                  2       nana
+```
+The suffix array for "banana" is {5, 3, 1, 0, 4, 2}
+
+In this section, we are discussing how to create a suffix array in O(N log N) time complexity.
+
+We use the concept of map. 
+
+```
+Algorithm is:
+
+1) Create a map with a key string and its value is integer.
+
+2) Iterate over the string in reverse order and create a new string(i.e from i = n - 1, 0).
+
+3) Map new string  with the last  index  position  of i.
+
+4) Create an array and assign all values of the map in the array.
+```
+
+The time complexity of the algorithm is O(N log N) because insertion in map takes O(log N) time and we are performing insertion n time so, the total time is O(N logN) where N is the length of the string.
+
+```C++
+// C++ program to build a suffix array in O(nlogn) time;
+#include <bits/stdc++.h>
+using namespace std;
+
+int main()
+{
+    string s = "banana";
+    int n = s.length();
+    map<string, int> Map;
+    int suffix[n];
+
+    // Maping string with its index of
+    // it's last letter.
+    string sub = "";
+    for (int i = n - 1; i >= 0; i--) {
+        sub = s[i] + sub;
+        Map[sub] = i;
+    }
+
+    // Storing all values of map
+    // in suffix array.
+    int j = 0;
+    for (auto x : Map) {
+        suffix[j] = x.second;
+        j++;
+    }
+
+    // printing suffix array.
+    cout << "Suffix array for banana is" << endl;
+    for (int i = 0; i < n; i++) {
+        cout << suffix[i] << " ";
+    }
+    cout << endl;
+    return 0;
+}
+```
+```
+Output
+
+Suffix array for banana is
+5 3 1 0 4 2 
+```
+
+### [Demo Link](https://replit.com/@Siddharthsing13/Suffix-arry#main.cpp).

Article/code.cpp

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+/*
+ * @Author: Siddharth Singh Chouhan.
+ * Git hub: Sid672.
+ */
+
+// C++ program to build a suffix array in O(nlogn) time;
+#include <bits/stdc++.h>
+using namespace std;
+
+int main()
+{
+    string s = "banana";
+    int n = s.length();
+    map<string, int> Map;
+    int suffix[n];
+
+    // Maping string with its index of
+    // it's last letter.
+    string sub = "";
+    for (int i = n - 1; i >= 0; i--) {
+        sub = s[i] + sub;
+        Map[sub] = i;
+    }
+
+    // Storing all values of map
+    // in suffix array.
+    int j = 0;
+    for (auto x : Map) {
+        suffix[j] = x.second;
+        j++;
+    }
+
+    // printing suffix array.
+    cout << "Suffix array for banana is" << endl;
+    for (int i = 0; i < n; i++) {
+        cout << suffix[i] << " ";
+    }
+    cout << endl;
+    return 0;
+}
+
+// Output
+
+// Suffix array for banana is
+// 5 3 1 0 4 2