[Pattern: Sliding Window][Hard] Smallest Window containing Substring

[Pei Yao-Chang]

Given a string and a pattern, find the smallest substring in the given string which has all the characters of the given pattern.

Example 1:

Input: String="aabdec", Pattern="abc"
Output: "abdec"
Explanation: The smallest substring having all characters of the pattern is "abdec"

Example 2:

Input: String="abdbca", Pattern="abc"
Output: "bca"
Explanation: The smallest substring having all characters of the pattern is "bca".

Example 3:

Input: String="adcad", Pattern="abc"
Output: ""
Explanation: No substring in the given string has all characters of the pattern.