adding string chapter

1 files changed, 26 insertions, 0 deletions

diff --git a/string/LCSubstring.cpp b/string/LCSubstring.cpp
new file mode 100644
index 0000000..69d636f
--- /dev/null
+++ b/string/LCSubstring.cpp
@@ -0,0 +1,26 @@
+//longest common substring.
+struct lcse {
+	int i = 0, s = 0;
+};
+string lcp(string s[2]) {
+	if(s[0].length() == 0 || s[1].length() == 0) return "";
+	vector<lcse> a(s[0].length()+s[1].length());
+	for(int k = 0; k < a.size(); k++) a[k].i=(k < s[0].length() ? k : k - s[0].length()), a[k].s = (k < s[0].length() ? 0 : 1);
+	sort(a.begin(), a.end(), [&] (const lcse &u, const lcse &l) {
+		int ui = u.i, li = l.i;
+		while(ui < s[u.s].length() && li < s[l.s].length()) {
+			if(s[u.s][ui] < s[l.s][li]) return true;
+			else if(s[u.s][ui] > s[l.s][li]) return false;
+			ui++; li++;
+		}
+		return !(ui < s[u.s].length());
+	});
+	int r = 0, m=0, c=0;
+	for(int i = 0; i < a.size() - 1; i++) { 
+		if(a[i].s == a[i+1].s) continue;
+		c = 0;
+		while(a[i].i+c < s[a[i].s].length() && a[i+1].i+c < s[a[i+1].s].length() && s[a[i].s][a[i].i+c] == s[a[i+1].s][a[i+1].i+c]) c++;
+		if(c > m) r=i, m=c;
+	}
+	return m == 0 ? "" : s[a[r].s].substr(a[r].i, m);
+}