3297. Count Substrings That Can Be Rearranged to Contain a String I
You are given two strings word1 and word2.
A string x is called valid if x can be rearranged to have word2 as a prefix.
Return the total number of valid substrings of word1.
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class Solution {
int helper(vector<vector<int>>& pre, vector<int>& f, int p) {
int l = p, r = pre.size() - 2, res = pre.size() - 1;
auto check = [&](int x) {
for(int i = 0; i < 26; i++) {
if(pre[x+1][i] - pre[p][i] < f[i]) return false;
}
return true;
};
while(l <= r) {
int m = l + (r - l) / 2;
bool ok = check(m);
if(ok) {
res = m;
r = m - 1;
} else l = m + 1;
}
return pre.size() - 1 - res;
}
public:
long long validSubstringCount(string word1, string word2) {
vector<int> freq(26);
for(auto& ch : word2) freq[ch-'a']++;
vector<int> now(26);
vector<vector<int>> pre{now};
for(int i = 0; i < word1.size(); i++) {
now[word1[i] - 'a']++;
pre.push_back(now);
}
long long res = 0;
for(int i = 0; i < word1.size(); i++) {
int now = helper(pre,freq,i);
if(!now) break;
res += now;
}
return res;
}
};
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