FastPrep
Problem · Dynamic Programming

Sum of All Values

● HardFlexportFULLTIMEOA

A school in HackerLand organized a scholarship exam with this interesting mathematics problem on addition.

Given a string num that consists of digits ('0' to '9'), a '+' can be inserted between its characters. No adjacent '+' characters are allowed. The value of the expression is then evaluated. Find the sum of the values of all possible expressions after inserting '+' characters any number of times (possibly zero). Since the answer can be large, return the value modulo (10^9 + 7).

Function Description

Complete the function getExpressionSums in the editor below.

getExpressionSums has the following parameter(s):

Examples
01 · Example 1
num = "123"
return = 168
All possible valid expressions are shown.
  • "1 + 23", value = 24
  • "12 + 3", value = 15
  • "1 + 2 + 3", value = 6
  • "123", value = 123
Their sum is 24 + 15 + 6 + 123 = 168. Thus, the answer is 168 modulo (10^9 + 7) which is 168.
Constraints
An unknown myth for now 🥲
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public int getExpressionSums(String num) {
    // write your code here
}
num"123"
expected168
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