diff --git a/.DS_Store b/.DS_Store
new file mode 100644
index 00000000..d4288847
Binary files /dev/null and b/.DS_Store differ
diff --git a/.gitignore b/.gitignore
index 2f0dd3cf..af679f82 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,4 @@
 /.nyc_output
 /npm-debug.log
 dist
+**/.DS_Store
diff --git a/package-lock.json b/package-lock.json
index af75e273..b64d1db0 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -483,6 +483,7 @@
       "resolved": "https://registry.npmjs.org/align-text/-/align-text-0.1.4.tgz",
       "integrity": "sha1-DNkKVhCT810KmSVsIrcGlDP60Rc=",
       "dev": true,
+      "optional": true,
       "requires": {
         "kind-of": "^3.0.2",
         "longest": "^1.0.1",
@@ -3854,7 +3855,8 @@
         "ansi-regex": {
           "version": "2.1.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "aproba": {
           "version": "1.2.0",
@@ -3875,12 +3877,14 @@
         "balanced-match": {
           "version": "1.0.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "brace-expansion": {
           "version": "1.1.11",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "balanced-match": "^1.0.0",
             "concat-map": "0.0.1"
@@ -3895,17 +3899,20 @@
         "code-point-at": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "concat-map": {
           "version": "0.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "console-control-strings": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "core-util-is": {
           "version": "1.0.2",
@@ -4022,7 +4029,8 @@
         "inherits": {
           "version": "2.0.3",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "ini": {
           "version": "1.3.5",
@@ -4034,6 +4042,7 @@
           "version": "1.0.0",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "number-is-nan": "^1.0.0"
           }
@@ -4048,6 +4057,7 @@
           "version": "3.0.4",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "brace-expansion": "^1.1.7"
           }
@@ -4055,12 +4065,14 @@
         "minimist": {
           "version": "0.0.8",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "minipass": {
           "version": "2.2.4",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "safe-buffer": "^5.1.1",
             "yallist": "^3.0.0"
@@ -4079,6 +4091,7 @@
           "version": "0.5.1",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "minimist": "0.0.8"
           }
@@ -4159,7 +4172,8 @@
         "number-is-nan": {
           "version": "1.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "object-assign": {
           "version": "4.1.1",
@@ -4171,6 +4185,7 @@
           "version": "1.4.0",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "wrappy": "1"
           }
@@ -4256,7 +4271,8 @@
         "safe-buffer": {
           "version": "5.1.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "safer-buffer": {
           "version": "2.1.2",
@@ -4292,6 +4308,7 @@
           "version": "1.0.2",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "code-point-at": "^1.0.0",
             "is-fullwidth-code-point": "^1.0.0",
@@ -4311,6 +4328,7 @@
           "version": "3.0.1",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "ansi-regex": "^2.0.0"
           }
@@ -4354,12 +4372,14 @@
         "wrappy": {
           "version": "1.0.2",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "yallist": {
           "version": "3.0.2",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         }
       }
     },
@@ -5193,7 +5213,8 @@
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/longest/-/longest-1.0.1.tgz",
       "integrity": "sha1-MKCy2jj3N3DoKUoNIuZiXtd9AJc=",
-      "dev": true
+      "dev": true,
+      "optional": true
     },
     "loose-envify": {
       "version": "1.4.0",
@@ -5640,6 +5661,7 @@
           "version": "0.1.4",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "kind-of": "^3.0.2",
             "longest": "^1.0.1",
@@ -5961,7 +5983,8 @@
         "is-buffer": {
           "version": "1.1.6",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "is-builtin-module": {
           "version": "1.0.0",
@@ -6045,6 +6068,7 @@
           "version": "3.2.2",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "is-buffer": "^1.1.5"
           }
@@ -6091,7 +6115,8 @@
         "longest": {
           "version": "1.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "lru-cache": {
           "version": "4.1.3",
@@ -6357,7 +6382,8 @@
         "repeat-string": {
           "version": "1.6.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "require-directory": {
           "version": "2.1.1",
diff --git a/src/.DS_Store b/src/.DS_Store
new file mode 100644
index 00000000..a3326275
Binary files /dev/null and b/src/.DS_Store differ
diff --git a/src/algorithms/.DS_Store b/src/algorithms/.DS_Store
new file mode 100644
index 00000000..7185f355
Binary files /dev/null and b/src/algorithms/.DS_Store differ
diff --git a/src/algorithms/string/.DS_Store b/src/algorithms/string/.DS_Store
new file mode 100644
index 00000000..ad874d49
Binary files /dev/null and b/src/algorithms/string/.DS_Store differ
diff --git a/src/algorithms/string/LongestCommLeadtrailSubString.js b/src/algorithms/string/LongestCommLeadtrailSubString.js
new file mode 100644
index 00000000..1d17a36d
--- /dev/null
+++ b/src/algorithms/string/LongestCommLeadtrailSubString.js
@@ -0,0 +1,45 @@
+/**
+ * Calculates Longest common leading and trailing substring of two numbers
+ * @param  {Number} a First string
+ * @param  {Number} b Second string
+ * @return {Number}   Longest common leading/trailing substring
+ */
+const LongestCommLeadtrailSubString = (str1, str2) => {
+        var leading = "";
+        var trailing = "";
+        var leadflag = false;
+        var trailflag = false;
+        if(str1.length ===0 || str2.length === 0){
+                console.log("Must enter valid strings")
+        }
+
+        var end1 = str1.length - 1
+        var end2 = str2.length - 1
+
+        let pos = 0
+
+        while (pos <= end1 && pos <= end2 && (leadflag === false || trailflag === false)) {
+                if (leadflag === false) {
+                        if (str1[pos] === str2[pos]) {
+                                leading = str1.substring(0, pos+1)
+                                
+                        }
+                        else{
+                                leadflag = true
+                        }
+                }
+                if (trailflag === false) {
+                        if (str1[end1 - pos] === str2[end2 - pos]) {
+                                trailing = str1.substring(end1 - pos)
+                                
+                        }
+                        else{
+                                trailflag = true;
+                        }
+                }
+                pos++
+        }
+        return {"leading":leading,"trailing": trailing}
+};
+
+module.exports = LongestCommLeadtrailSubString;
\ No newline at end of file
diff --git a/test/.DS_Store b/test/.DS_Store
new file mode 100644
index 00000000..d9c3af28
Binary files /dev/null and b/test/.DS_Store differ
diff --git a/test/algorithms/.DS_Store b/test/algorithms/.DS_Store
new file mode 100644
index 00000000..30b048b2
Binary files /dev/null and b/test/algorithms/.DS_Store differ
diff --git a/test/algorithms/string/testleadtrail.js b/test/algorithms/string/testleadtrail.js
new file mode 100644
index 00000000..47da7230
--- /dev/null
+++ b/test/algorithms/string/testleadtrail.js
@@ -0,0 +1,38 @@
+/* eslint-env mocha */
+const LongestCommLeadtrailSubString = require('../../../src/algorithms/string/LongestCommLeadtrailSubString');
+const expect = require('expect');
+
+
+describe('Longest common leading and trailing substring of two strings', () => {
+  it('should return empty strings if the inputs mismatch entirely', () => {
+    const stringA = 'ABCDEF';
+    const stringB = 'QRST';
+
+    const SubStrings = LongestCommLeadtrailSubString(stringA, stringB);
+    expect(SubStrings).toStrictEqual({"leading":"","trailing": ""});
+  });
+
+  it('should return only trailing common substring if no leading common subtring found', () => {
+    const stringA = 'ABCMNOP';
+    const stringB = 'EFGHMNOP';
+
+    const SubStrings = LongestCommLeadtrailSubString(stringA, stringB);
+    expect(SubStrings).toStrictEqual({"leading":"","trailing": "MNOP"});
+  });
+
+  it('should return only leading common substring if no trailing common subtring found', () => {
+    const stringA = 'ABCMNOP';
+    const stringB = 'ABCYZ';
+
+    const SubStrings = LongestCommLeadtrailSubString(stringA, stringB);
+    expect(SubStrings).toStrictEqual({"leading":"ABC","trailing": ""});
+  });
+
+  it('should return both leading common substring and trailing common subtring if found', () => {
+    const stringA = 'ABCYEFG';
+    const stringB = 'ABCZEFG';
+
+    const SubStrings = LongestCommLeadtrailSubString(stringA, stringB);
+    expect(SubStrings).toStrictEqual({"leading":"ABC","trailing": "EFG"});
+  });
+});