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Author: assassint2017

Implement strStr()/Implement_strStr().cpp

@@ -0,0 +1,46 @@
+// 这道题目完全在考察KMP算法
+// Runtime: 4 ms, faster than 91.22% of C++ online submissions for Implement strStr().
+// Memory Usage: 9.3 MB, less than 21.43% of C++ online submissions for Implement strStr().
+
+class Solution
+{
+public:
+	int strStr(string s, string p)
+	{
+		// 边界条件处理
+		if (p.length() == 0) return 0;
+        if (s.length() == 0 && p.length() != 0) return -1;
+
+		// 获取next数组
+		vector<int> next(p.length());
+		getNext(next, p);
+
+		// KMP
+		int i = 0, j = 0;
+		while (i < s.length() && j < static_cast<int>(p.size())
+		{
+			if (j == -1 || s[i] == p[j])
+				++i, ++j;
+			else
+				j = next[j];
+		}
+		return j == p.length() ? i - j : -1;
+	}
+private:
+	void getNext(vector<int>& next, const string& p) 
+	{
+		next[0] = -1;
+		int i = 0, j = -1;
+
+		while (i < p.length() - 1) 
+		{
+			if (j == -1 || p[i] == p[j]) 
+			{
+				++i, ++j;
+				next[i] = j;
+			}
+			else 
+				j = next[j];
+		}
+	}
+};