# 2478. Number of Beautiful Partitions

## Description

You are given a string s that consists of the digits '1' to '9' and two integers k and minLength.

A partition of s is called beautiful if:

• s is partitioned into k non-intersecting substrings.
• Each substring has a length of at least minLength.
• Each substring starts with a prime digit and ends with a non-prime digit. Prime digits are '2', '3', '5', and '7', and the rest of the digits are non-prime.

Return the number of beautiful partitions of s. Since the answer may be very large, return it modulo 109 + 7.

A substring is a contiguous sequence of characters within a string.

Example 1:

Input: s = "23542185131", k = 3, minLength = 2
Output: 3
Explanation: There exists three ways to create a beautiful partition:
"2354 | 218 | 5131"
"2354 | 21851 | 31"
"2354218 | 51 | 31"


Example 2:

Input: s = "23542185131", k = 3, minLength = 3
Output: 1
Explanation: There exists one way to create a beautiful partition: "2354 | 218 | 5131".


Example 3:

Input: s = "3312958", k = 3, minLength = 1
Output: 1
Explanation: There exists one way to create a beautiful partition: "331 | 29 | 58".


Constraints:

• 1 <= k, minLength <= s.length <= 1000
• s consists of the digits '1' to '9'.

## Solutions

• class Solution {
private static final int MOD = (int) 1e9 + 7;

public int beautifulPartitions(String s, int k, int minLength) {
int n = s.length();
if (!prime(s.charAt(0)) || prime(s.charAt(n - 1))) {
return 0;
}
int[][] f = new int[n + 1][k + 1];
int[][] g = new int[n + 1][k + 1];
f[0][0] = 1;
g[0][0] = 1;
for (int i = 1; i <= n; ++i) {
if (i >= minLength && !prime(s.charAt(i - 1)) && (i == n || prime(s.charAt(i)))) {
for (int j = 1; j <= k; ++j) {
f[i][j] = g[i - minLength][j - 1];
}
}
for (int j = 0; j <= k; ++j) {
g[i][j] = (g[i - 1][j] + f[i][j]) % MOD;
}
}
return f[n][k];
}

private boolean prime(char c) {
return c == '2' || c == '3' || c == '5' || c == '7';
}
}

• class Solution {
public:
const int mod = 1e9 + 7;

int beautifulPartitions(string s, int k, int minLength) {
int n = s.size();
auto prime = [](char c) {
return c == '2' || c == '3' || c == '5' || c == '7';
};
if (!prime(s[0]) || prime(s[n - 1])) return 0;
vector<vector<int>> f(n + 1, vector<int>(k + 1));
vector<vector<int>> g(n + 1, vector<int>(k + 1));
f[0][0] = g[0][0] = 1;
for (int i = 1; i <= n; ++i) {
if (i >= minLength && !prime(s[i - 1]) && (i == n || prime(s[i]))) {
for (int j = 1; j <= k; ++j) {
f[i][j] = g[i - minLength][j - 1];
}
}
for (int j = 0; j <= k; ++j) {
g[i][j] = (g[i - 1][j] + f[i][j]) % mod;
}
}
return f[n][k];
}
};

• class Solution:
def beautifulPartitions(self, s: str, k: int, minLength: int) -> int:
primes = '2357'
if s[0] not in primes or s[-1] in primes:
return 0
mod = 10**9 + 7
n = len(s)
f = [[0] * (k + 1) for _ in range(n + 1)]
g = [[0] * (k + 1) for _ in range(n + 1)]
f[0][0] = g[0][0] = 1
for i, c in enumerate(s, 1):
if i >= minLength and c not in primes and (i == n or s[i] in primes):
for j in range(1, k + 1):
f[i][j] = g[i - minLength][j - 1]
for j in range(k + 1):
g[i][j] = (g[i - 1][j] + f[i][j]) % mod
return f[n][k]


• func beautifulPartitions(s string, k int, minLength int) int {
prime := func(c byte) bool {
return c == '2' || c == '3' || c == '5' || c == '7'
}
n := len(s)
if !prime(s[0]) || prime(s[n-1]) {
return 0
}
const mod int = 1e9 + 7
f := make([][]int, n+1)
g := make([][]int, n+1)
for i := range f {
f[i] = make([]int, k+1)
g[i] = make([]int, k+1)
}
f[0][0], g[0][0] = 1, 1
for i := 1; i <= n; i++ {
if i >= minLength && !prime(s[i-1]) && (i == n || prime(s[i])) {
for j := 1; j <= k; j++ {
f[i][j] = g[i-minLength][j-1]
}
}
for j := 0; j <= k; j++ {
g[i][j] = (g[i-1][j] + f[i][j]) % mod
}
}
return f[n][k]
}

• function beautifulPartitions(s: string, k: number, minLength: number): number {
const prime = (c: string): boolean => {
return c === '2' || c === '3' || c === '5' || c === '7';
};

const n: number = s.length;
if (!prime(s[0]) || prime(s[n - 1])) return 0;

const f: number[][] = new Array(n + 1).fill(0).map(() => new Array(k + 1).fill(0));
const g: number[][] = new Array(n + 1).fill(0).map(() => new Array(k + 1).fill(0));
const mod: number = 1e9 + 7;

f[0][0] = g[0][0] = 1;

for (let i = 1; i <= n; ++i) {
if (i >= minLength && !prime(s[i - 1]) && (i === n || prime(s[i]))) {
for (let j = 1; j <= k; ++j) {
f[i][j] = g[i - minLength][j - 1];
}
}
for (let j = 0; j <= k; ++j) {
g[i][j] = (g[i - 1][j] + f[i][j]) % mod;
}
}

return f[n][k];
}