packagehard;

publicclassMinimumWindowSubstring {

publicStringminWindow(Strings,Stringt) {

int[]counts =newint[256];

for(charc :t.toCharArray()){

counts[c]++;

}

intstart =0,end =0,minStart =0,minLen =Integer.MAX_VALUE,counter =t.length();

while(end <s.length()){

if(counts[s.charAt(end)] >0)counter--;

counts[s.charAt(end)]--;

end++;

while(counter ==0){

if(end-start <minLen){

minStart =start;

minLen =end-start;

}

counts[s.charAt(start)]++;

if(counts[s.charAt(start)] >0)counter++;

start++;

}

}

if(minLen ==Integer.MAX_VALUE)return"";

returns.substring(minStart,minStart+minLen);

}

}

|278|[First Bad Version](https://leetcode.com/problems/first-bad-version/)|[Solution](../../blob/master/EASY/src/easy/FirstBadVersion.java)| O(logn)|O(1) | Easy| Binary Search

|133|[Clone Graph](https://leetcode.com/problems/clone-graph/)|[Solution](../../blob/master/MEDIUM/src/medium/CloneGraph.java)| O(n)|O(n) | Medium| HashMap, BFS

|91|[Decode Ways](https://leetcode.com/problems/decode-ways/)|[Solution](../../blob/master/MEDIUM/src/medium/DecodeWays.java)| O(n)|O(n) | Medium| DP

|76|[Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/)|[Solution](../../blob/master/HARD/src/hard/MinimumWindowSubstring.java)|O(n)|O(k)|Hard|Two Pointers

|23|[Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/)|[Solution](../../blob/master/HARD/src/hard/MergeKSortedList.java)|O(n*logk)|O(logk)|Hard|Heap

|17|[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)|[Solution](../../blob/master/MEDIUM/src/medium/LetterCombinationsofaPhoneNumber.java)|O(n*4^n)|O(n)|Medium|Backtracking

|10|[Regular Expression Matching](https://leetcode.com/problems/regular-expression-matching/)|[Solution](../../blob/master/HARD/src/hard/RegularExpressionMatching.java)|O(m*n)|O(m*n)|Hard|DP