FastPrep
Problem · String

Get Substring

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Problem statement

There is a string input_str consisting of characters '0' and '1' only and an integer k. Find a substring of input_str such that:

  • The number of '1's is equal to k
  • It has the smallest length
  • It is lexicographically smallest

Note: It is guaranteed that answer always exists.

Function

getSubstring(input_str: String, k: int) → String

Complete the function getSubstring in the editor below.

getSubstring has the following parameters:

  • string input_str: a string that consists of '0' and '1'
  • int k: the number of '1's in the answer

Returns

string: the substring that meets the given conditions

Examples

Example 1

input_str = "0101101"k = 3return = "1011"
Some of the possible substrings following the first condition:
  • "01011"
  • "1101"
  • "1011"
The substring that is smallest in length and lexicographically smallest is "1011". It can be proven that there is no other substring that is smaller than "1011" in length and lexicographic order. Hence the answer is "1011".

Constraints

  • 1 ≤ k ≤ length of input_str ≤ 10^3
  • input_str[i] is in the set {'0', '1'}
  • The number of '1' characters in string input_str is always greater than or equal to k.

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    public String getSubstring(String input_str, int k) {
  // write your code here
}
    input_str"0101101"
    k3
    expected"1011"
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