Create 828.cpp

LeetCode-CN/828.cpp

@@ -0,0 +1,35 @@
+class Solution {
+public:
+	const static long long MOD = 1000000007;
+	int uniqueLetterString(string S) {
+		map<char, vector<int>> mp;
+		long long cnt = 0;
+		int slen = S.size();
+		for (int i = 0; i < slen; i++)
+		{
+			auto iter = mp.find(S[i]);
+			if (iter == mp.end())
+			{
+				tie(iter, ignore) = mp.insert(make_pair(S[i], vector<int>{-1}));
+				
+			}
+			else
+			{
+				int sz = iter->second.size();
+				int k = iter->second[sz - 2];
+				int j = iter->second[sz - 1];
+				cnt = (cnt + (j - k)*(i - j)) % MOD;
+			}
+			iter->second.push_back(i);
+		}
+		for (const auto& pr : mp)
+		{
+			int sz = pr.second.size();
+			int k = pr.second[sz - 2];
+			int j = pr.second[sz - 1];
+			cnt = (cnt + (j - k)*(slen - j)) % MOD;
+		}
+
+		return cnt;
+	}
+};