### PROBLEM LINK:

**Author:** Rezwanul Islam Maruf

### DIFFICULTY:

MEDIUM

### PREREQUISITES:

DP, Math

### PROBLEM:

Each charter has assigned by an integer number. Need to find the number of string with length L which charters are sorted with no duplicates charter and sum of the charters is S.

### QUICK EXPLANATION:

L and S is large. But with some observation **no duplicates charter**, we can say that string length should be less or equal 52 (number of lower case and upper case English letter). And that means no string with S greater then 1378.

So dp array should be dp[52][1378]. And the dp should be like classical 0-1 knapsack algorithm when charters are the items and S is the weight.

### AUTHORâ€™S SOLUTIONS:

Authorâ€™s solution can be found here.