[#2] Add ABC_162_D

cp-study/atcoder-study#21

Author: zeikar

ABC_162_D.cpp

@@ -0,0 +1,54 @@
+#include <iostream>
+#include <string>
+using namespace std;
+
+int main() {
+	int n;
+	string s;
+	long long result;
+
+	cin >> n >> s;
+
+	// step 1, count rgb triplets
+	long long cntR = 0, cntG = 0, cntB = 0;
+
+	for (int i = 0; i < n; i++)
+	{
+		if (s[i] == 'R')
+		{
+			cntR++;
+		}
+		else if (s[i] == 'G')
+		{
+			cntG++;
+		}
+		else
+		{
+			cntB++;
+		}
+	}
+
+	result = cntR * cntG * cntB;
+
+	// step 2, count j-i == k-j
+	for (int i = 0; i < n; i++)
+	{
+		for (int offset = 1; offset < n; offset++)
+		{
+			int j = i + offset;
+			int k = j + offset;
+
+			if (k >= n)
+			{
+				continue;
+			}
+
+			if (s[i] != s[j] && s[j] != s[k] && s[i] != s[k])
+			{
+				result--;
+			}
+		}
+	}
+
+	cout << result << endl;
+}