diff --git a/Longest-Common-Substring.cpp b/Longest-Common-Substring.cpp
new file mode 100644
index 0000000..d398f75
--- /dev/null
+++ b/Longest-Common-Substring.cpp
@@ -0,0 +1,143 @@
+#include <cstdio>
+#include <cstring>
+
+#define STRING_LENGTH 300000
+
+using namespace std;
+
+struct sortinfo
+{
+	int x, y, ord;
+};
+
+int l;
+char s[STRING_LENGTH], t[STRING_LENGTH / 2];
+int rank[STRING_LENGTH * 2], sa[STRING_LENGTH], height[STRING_LENGTH];
+
+void radix_sort(sortinfo *d)
+{
+	static sortinfo _d[STRING_LENGTH], res[STRING_LENGTH];
+	static int c[STRING_LENGTH];
+	memset(c, 0, sizeof(c));
+	for (int i = 0; i < l; i++)
+	{
+		c[d[i].y]++;
+	}
+	for (int i = 1; i <= l; i++)
+	{
+		c[i] += c[i - 1];
+	}
+	for (int i = l - 1; i >= 0; i--)
+	{
+		_d[--c[d[i].y]] = d[i];
+	}
+	memset(c, 0, sizeof(c));
+	for (int i = 0; i < l; i++)
+	{
+		c[_d[i].x]++;
+	}
+	for (int i = 1; i <= l; i++)
+	{
+		c[i] += c[i - 1];
+	}
+	for (int i = l - 1; i >= 0; i--)
+	{
+		res[--c[_d[i].x]] = _d[i];
+	}
+	for (int i = 0; i < l; i++)
+	{
+		d[i] = res[i];
+	}
+}
+
+void init_rank()
+{
+	static int c[256];
+	static sortinfo d[STRING_LENGTH];
+	int x = 1;
+	for (int i = 0; i < l; i++)
+	{
+		c[(int)s[i]] = 1;
+	}
+	for (int i = 0; i < 256; i++)
+	{
+		if (c[i] == 1)
+		{
+			c[i] = x++;
+		}
+	}
+	for (int i = 0; i < l; i++)
+	{
+		rank[i] = c[(int)s[i]];
+	}
+	for (int k = 1; k < l; k <<= 1)
+	{
+		for (int i = 0; i < l; i++)
+		{
+			d[i].x = rank[i];
+			d[i].y = rank[i + k];
+			d[i].ord = i;
+		}
+		radix_sort(d);
+		x = 1;
+		rank[d[0].ord] = 1;
+		for (int i = 1; i < l; i++)
+		{
+			rank[d[i].ord] = (d[i].x == d[i - 1].x && d[i].y == d[i - 1].y ? x : ++x);
+		}
+		if (x == l)
+		{
+			break;
+		}
+	}
+}
+
+void rank_to_sa()
+{
+	for (int i = 0; i < l; i++)
+	{
+		sa[rank[i]] = i;
+	}
+}
+
+void init_height()
+{
+	int k = 0;
+	for (int i = 0; i < l; i++)
+	{
+		if (k > 0)
+		{
+			k--;
+		}
+		if (rank[i] == l)
+		{
+			continue;
+		}
+		for (; s[i + k] == s[sa[rank[i] + 1] + k]; k++) ;
+		height[rank[i]] = k;
+	}
+}
+
+int main()
+{
+	int l1, l2;
+	scanf("%s%s", s, t);
+	l1 = strlen(s);
+	l2 = strlen(t);
+	s[l1] = '#';
+	strcat(s, t);
+	l = l1 + l2;
+	init_rank();
+	rank_to_sa();
+	init_height();
+	int maxlen = 0;
+	for (int i = 1; i < l; i++)
+	{
+		if (height[i] > maxlen && ((sa[i] < l1 && sa[i + 1] > l1) || (sa[i] > l1 && sa[i + 1] < l1)))
+		{
+			maxlen = height[i];
+		}
+	}
+	printf("%d", maxlen);
+	return 0;
+}