### PROBLEM LINK:

**Author:** Bhuvnesh Jain

**Tester:** Bhuvnesh Jain

**Editorialist:** Bhuvnesh Jain

### DIFFICULTY:

CAKEWALK

### PREREQUISITES:

Modular Exponentiation

### PROBLEM:

String **a** to be strictly greater than String **b** (both are of same length) when each character of a is strictly greater than corresponding character in b.

For the string length l, you have to calculate how many pairs (x, y) exist such that string x is strictly greater than string y.

### EXPLANATION:

Consider the case when the lenth of the string is **l==1**. Here the answer is 325 because the number of pairs

*with a as first part are b, c, d, e,…x, y, z i.e. 25 in number*

*with b as the first part are c, d, e, f, …x, y, z i.e. 24 in number. and so on.*

Total number of required pairs = \sum_{i=0}^{25}{i} = \frac{25.26}{2} = 325

So let us generalise the formula for length **l==n**

Total number of required pairs = \sum_{i_1=0}^{25}{\sum_{i_2=0}^{25} \cdots \sum_{i_n=0}^{25} i_1.i_2 \cdots i_n} = \sum_{i_1=0}^{25}{i_1} . \sum_{i_2=0}^{25}{i_2} \cdots \sum_{i_n=0}^{25}{i_n} = 325^n

Hence, we just need to find **325^n modulo (10^9 + 7)**, which can be done easily using modular exponentiation.

### COMPLEXITY

O(logn) per test case.

### AUTHOR’S SOLUTION:

Author’s solution can be found here.