leetcode 日经贴，Cpp code -Minimum Window Substring

class Solution {
public:
string minWindow(string s, string t) {
vector<int> count(256);
int st = -1, ed = s.length(), distinct = 0;
for (int i = 0; i < t.length(); ++i) {
if (++count[t[i]] == 1) {
++distinct;
}
}
int p1 = 0;
int n = s.length();
for (int i = 0; i < n; ++i) {
if (--count[s[i]] == 0) {
--distinct;
}
if (distinct == 0) {
while (p1 < i && count[s[p1]] < 0) {
++count[s[p1++]];
}
if (i - p1 < ed - st) {
st = p1;
ed = i;
}
}
}
if (st == -1) {
return "";
}
return s.substr(st, ed - st + 1);
}
};