LeetCode Minimum Window Substring

class Solution {
private:
int shd_cnt[256];
int cur_cnt[256];
public:
string minWindow(string S, string T) {
int slen = S.length();
int tlen = T.length();

// array to store char stat info of string T
for (int i=0; i<256; i++) shd_cnt[i] = cur_cnt[i] = 0;
// collect char stat info of string T
for (int i=0; i<tlen; i++) shd_cnt[T[i]]++;

int shd_match_cnt = 0, cur_match_cnt = 0;
for (int i=0; i<256; i++) shd_match_cnt += shd_cnt[i] != 0;

int start = 0, end = 0;

int mlen = INT_MAX, ps = 0, pe = 0;

bool updated = true;

while (updated) {
updated = false;
while (cur_match_cnt == shd_match_cnt && start < slen) {
if (end - start < mlen) {
mlen = end - start;
ps = start, pe = end;
}

char ch = S[start];
// whether current char is critical for matching
// if so it could not be omitted
if (cur_cnt[ch] - 1 < shd_cnt[ch]) break;

updated = true;
cur_cnt[ch]--;
start++;
}

if (end < slen) {
updated = true;
char ch = S[end++];

if (++cur_cnt[ch] == shd_cnt[ch]) { // using strict equal
cur_match_cnt++;
}
}
}
return S.substr(ps, pe - ps);
}
};

class Solution {
public:
string minWindow(string s, string t) {
int cnt[128] = {0};
int distinct = 0;
int slen = s.size();
int tlen = t.size();

for (int i=0; i<tlen; i++) {
if (!cnt[t[i]]++) {
distinct++;
}
}
int matched = 0;
int mcnt[128] = {0};
int p=0;
int q=0;

int minlen = INT_MAX;
int minstart = 0;

while (q < slen) {
char ch = s[q];
if (cnt[ch]) {
if (++mcnt[ch] == cnt[ch]) {
matched++;
}
}
q++;
if (matched != distinct) {
continue;
}
while (p < q) {
if (!cnt[s[p]]) {
p++;
continue;
}
if (mcnt[s[p]] > cnt[s[p]]) {
mcnt[s[p]]--;
p++;
} else {
break;
}
}

if (q - p < minlen) {
minstart = p;
minlen = q - p;
}
}
minlen = distinct == matched ? minlen : 0;
return s.substr(minstart, minlen);
}
};