lanqiao3514 字串简写

14lanqiao/test7-2.cpp

@@ -0,0 +1,21 @@
+// lanqiao3514 字串简写(前缀和优化)
+#include<bits/stdc++.h>
+using namespace std;
+#define int long long
+signed main(){
+    int k;
+    string s;
+    char a, b;
+    cin >> k >> s >> a >> b;
+    int ft = 0;
+    int bk = 0;
+    for(int i = 0, j = k - 1; j < s.size(); i++, j++){
+        if(s[i] == a) ft++;
+        if(s[j] == b) bk += ft;
+    }
+    cout << bk << endl;
+}
+/* samples -> 6
+4
+abababdb a b
+*/