leetcode - Minimum Window Substring

Given a string S and a string T, find the minimum window in S which will contain all the characters in T in complexity O(n).

For example,

S =

"ADOBECODEBANC"

T =

"ABC"

Minimum window is

"BANC"

.

Note:

If there is no such window in S that covers all characters in T, return the emtpy string

""

.

If there are multiple such windows, you are guaranteed that there will always be only one unique minimum window in S.

class Solution {
public:
std::string minWindow(std::string S, std::string T) {
if (S.empty() || T.empty())
{
return "";
}
int count = T.size();
int require[128] = {0};
bool chSet[128] = {false};
for (int i = 0; i < count; ++i)
{
require[T[i]]++;
chSet[T[i]] = true;
}
int i = -1;
int j = 0;
int minLen = INT_MAX;
int minIdx = 0;
while (i < (int)S.size() && j < (int)S.size())
{
if (count)
{
i++;
require[S[i]]--;
if (chSet[S[i]] && require[S[i]] >= 0)
{
count--;
}
}
else
{
if (minLen > i - j + 1)
{
minLen = i - j + 1;
minIdx = j;
}
require[S[j]]++;
if (chSet[S[j]] && require[S[j]] > 0)
{
count++;
}
j++;
}
}
if (minLen == INT_MAX)
{
return "";
}
return S.substr(minIdx, minLen);
}
};