Find the Suffix Array of given String with no repeating character
Last Updated :
24 Feb, 2022
Given a string str of size N, the task is to find the suffix array of the given string.
Note: A suffix array is a sorted array of all suffixes of a given string.
Examples:
Input: str = “prince”
Output: 4 5 2 3 0 1
Explanation: The suffixes are
0 prince 4 ce
1 rince Sort the suffixes 5 e
2 ince —————-> 2 ince
3 nce alphabetically 3 nce
4 ce 0 prince
5 e 1 rince
Input: str = “abcd”
Output: 0 1 2 3
Approach: The methods of suffix array finding for any string are discussed here. In this article, the focus is on finding suffix array for strings with no repeating character. It is a simple implementation based problem. Follow the steps mentioned below to solve the problem:
- Count occurrence of each character.
- Find prefix sum of it.
- Find start array by start[0] = 0, start[i+1] = prefix[i] for all i > 0 .
- Find start array containing the index of the substring (suffix) with starting character of the respective column.
Follow the illustration below for better understanding.
Illustration:
Consider string “prince”:
Given below is the suffix table
| char |
a |
b |
c |
d |
e |
f |
g |
h |
i |
j |
k |
l |
m |
n |
o |
p |
q |
r |
s |
t |
u |
v |
w |
x |
y |
z |
| count |
0 |
0 |
1 |
0 |
1 |
0 |
0 |
0 |
1 |
0 |
0 |
0 |
0 |
1 |
0 |
1 |
0 |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
| prefix |
0 |
0 |
1 |
1 |
2 |
2 |
2 |
2 |
3 |
3 |
3 |
3 |
3 |
4 |
4 |
5 |
5 |
6 |
6 |
6 |
6 |
6 |
6 |
6 |
6 |
6 |
| start |
0 |
0 |
0 |
1 |
1 |
2 |
2 |
2 |
2 |
3 |
3 |
3 |
3 |
3 |
4 |
4 |
5 |
5 |
6 |
6 |
6 |
6 |
6 |
6 |
6 |
6 |
For char ‘r’ start value is 5 .
Implies substring (suffix) starting with char ‘r’ i.e. “rince” has rank 5 .
Rank is position in suffix array. ( 1 “rince” ) implies 5th position in suffix array ), refer first table.
Similarly, start value of char ‘n’ is 3 . Implies ( 3 “nce” ) 3rd position in suffix array .
Below is the implementation of the above approach
C++
#include <bits/stdc++.h>
using namespace std;
void suffixArray(string str, int N)
{
int arr[30] = { 0 };
for (int i = 0; i < N; i++) {
arr[str[i] - 'a']++;
}
for (int i = 1; i < 30; i++) {
arr[i] = arr[i] + arr[i - 1];
}
int start[30];
start[0] = 0;
for (int i = 0; i < 29; i++) {
start[i + 1] = arr[i];
}
int ans[N] = { 0 };
for (int i = N - 1; i >= 0; i--) {
ans[start[str[i] - 'a']] = i;
}
for (int i = 0; i < N; i++)
cout << ans[i] << " ";
}
int main()
{
string str = "prince";
int N = str.length();
suffixArray(str, N);
return 0;
}
|
Java
import java.io.*;
import java.lang.*;
import java.util.*;
class GFG {
static void suffixArray(String str, int N)
{
int arr[] = new int[30];
for (int i = 0; i < N; i++) {
arr[str.charAt(i) - 'a']++;
}
for (int i = 1; i < 30; i++) {
arr[i] = arr[i] + arr[i - 1];
}
int start[] = new int[30];
start[0] = 0;
for (int i = 0; i < 29; i++) {
start[i + 1] = arr[i];
}
int ans[] = new int[N];
for (int i = N - 1; i >= 0; i--) {
ans[start[str.charAt(i) - 'a']] = i;
}
for (int i = 0; i < N; i++)
System.out.print(ans[i] + " ");
}
public static void main (String[] args)
{
String str = "prince";
int N = str.length();
suffixArray(str, N);
}
}
|
Python3
def suffixArray(str, N):
arr = [0] * 30
for i in range(N):
arr[ord(str[i]) - ord('a')] += 1
for i in range(1, 30):
arr[i] = arr[i] + arr[i - 1]
start = [0] * 30
start[0] = 0
for i in range(29):
start[i + 1] = arr[i]
ans = [0] * N
for i in range(N - 1, 0, -1):
ans[start[ord(str[i]) - ord('a')]] = i
for i in range(N):
print(ans[i], end=" ")
str = "prince"
N = len(str)
suffixArray(str, N)
|
C#
using System;
class GFG
{
static void suffixArray(string str, int N)
{
int[] arr = new int[30];
for (int i = 0; i < N; i++) {
arr[str[i] - 'a']++;
}
for (int i = 1; i < 30; i++) {
arr[i] = arr[i] + arr[i - 1];
}
int[] start = new int[30];
start[0] = 0;
for (int i = 0; i < 29; i++) {
start[i + 1] = arr[i];
}
int[] ans = new int[N];
for (int i = N - 1; i >= 0; i--) {
ans[start[str[i] - 'a']] = i;
}
for (int i = 0; i < N; i++) {
Console.Write(ans[i]);
Console.Write(" ");
}
}
public static int Main()
{
string str = "prince";
int N = str.Length;
suffixArray(str, N);
return 0;
}
}
|
Javascript
<script>
function suffixArray(str, N) {
let arr = new Array(30).fill(0);
for (let i = 0; i < N; i++) {
arr[str[i].charCodeAt(0) - 'a'.charCodeAt(0)]++;
}
for (let i = 1; i < 30; i++) {
arr[i] = arr[i] + arr[i - 1];
}
let start = new Array(30)
start[0] = 0;
for (let i = 0; i < 29; i++) {
start[i + 1] = arr[i];
}
let ans = new Array(N).fill(0)
for (let i = N - 1; i >= 0; i--) {
ans[start[str[i].charCodeAt(0) - 'a'.charCodeAt(0)]] = i;
}
for (let i = 0; i < N; i++)
document.write(ans[i] + " ")
}
let str = "prince";
let N = str.length;
suffixArray(str, N);
</script>
|
Time Complexity: O(N)
Auxiliary Space: O(N)
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