From 5e8edafbe1523ab3e353c014e848dfcdd0cdcfd3 Mon Sep 17 00:00:00 2001
From: Ilya Kantor <iliakan@gmail.com>
Date: Wed, 24 Jul 2019 11:58:06 +0300
Subject: [PATCH] regexp task

---
 .../solution.md                               |  0
 .../task.md                                   |  2 +-
 .../solution.md                               | 18 ------------
 .../3-find-decimal-positive-numbers/task.md   | 12 --------
 .../1-find-non-negative-integers/solution.md  | 28 +++++++++++++++++++
 .../1-find-non-negative-integers/task.md      | 14 ++++++++++
 6 files changed, 43 insertions(+), 31 deletions(-)
 rename 9-regular-expressions/09-regexp-groups/{4-find-decimal-numbers => 2-find-decimal-numbers}/solution.md (100%)
 rename 9-regular-expressions/09-regexp-groups/{4-find-decimal-numbers => 2-find-decimal-numbers}/task.md (91%)
 delete mode 100644 9-regular-expressions/09-regexp-groups/3-find-decimal-positive-numbers/solution.md
 delete mode 100644 9-regular-expressions/09-regexp-groups/3-find-decimal-positive-numbers/task.md
 create mode 100644 9-regular-expressions/14-regexp-lookahead-lookbehind/1-find-non-negative-integers/solution.md
 create mode 100644 9-regular-expressions/14-regexp-lookahead-lookbehind/1-find-non-negative-integers/task.md

diff --git a/9-regular-expressions/09-regexp-groups/4-find-decimal-numbers/solution.md b/9-regular-expressions/09-regexp-groups/2-find-decimal-numbers/solution.md
similarity index 100%
rename from 9-regular-expressions/09-regexp-groups/4-find-decimal-numbers/solution.md
rename to 9-regular-expressions/09-regexp-groups/2-find-decimal-numbers/solution.md
diff --git a/9-regular-expressions/09-regexp-groups/4-find-decimal-numbers/task.md b/9-regular-expressions/09-regexp-groups/2-find-decimal-numbers/task.md
similarity index 91%
rename from 9-regular-expressions/09-regexp-groups/4-find-decimal-numbers/task.md
rename to 9-regular-expressions/09-regexp-groups/2-find-decimal-numbers/task.md
index 121a18a4..44656384 100644
--- a/9-regular-expressions/09-regexp-groups/4-find-decimal-numbers/task.md
+++ b/9-regular-expressions/09-regexp-groups/2-find-decimal-numbers/task.md
@@ -1,4 +1,4 @@
-# Find all numbers
+# Find decimal numbers
 
 Write a regexp that looks for all decimal numbers including integer ones, with the floating point and negative ones.
 
diff --git a/9-regular-expressions/09-regexp-groups/3-find-decimal-positive-numbers/solution.md b/9-regular-expressions/09-regexp-groups/3-find-decimal-positive-numbers/solution.md
deleted file mode 100644
index c99a95bb..00000000
--- a/9-regular-expressions/09-regexp-groups/3-find-decimal-positive-numbers/solution.md
+++ /dev/null
@@ -1,18 +0,0 @@
-
-An non-negative integer number is `pattern:\d+`. A zero `0` can't be the first digit,  but we should allow it in further digits.
-
-So that gives us `pattern:[1-9]\d*`.
-
-A decimal part is: `pattern:\.\d+`.
-
-Because the decimal part is optional, let's put it in parentheses with the quantifier `pattern:?`.
-
-Finally we have the regexp: `pattern:[1-9]\d*(\.\d+)?`:
-
-```js run
-let reg = /[1-9]\d*(\.\d+)?/g;
-
-let str = "1.5 0 -5 12. 123.4.";
-
-alert( str.match(reg) );   // 1.5, 0, 12, 123.4
-```
diff --git a/9-regular-expressions/09-regexp-groups/3-find-decimal-positive-numbers/task.md b/9-regular-expressions/09-regexp-groups/3-find-decimal-positive-numbers/task.md
deleted file mode 100644
index ad8c81ea..00000000
--- a/9-regular-expressions/09-regexp-groups/3-find-decimal-positive-numbers/task.md
+++ /dev/null
@@ -1,12 +0,0 @@
-# Find positive numbers
-
-Create a regexp that looks for positive numbers, including those without a decimal point.
-
-An example of use:
-```js
-let reg = /your regexp/g;
-
-let str = "1.5 0 -5 12. 123.4.";
-
-alert( str.match(reg) ); // 1.5, 12, 123.4 (ignores 0 and -5)
-```
diff --git a/9-regular-expressions/14-regexp-lookahead-lookbehind/1-find-non-negative-integers/solution.md b/9-regular-expressions/14-regexp-lookahead-lookbehind/1-find-non-negative-integers/solution.md
new file mode 100644
index 00000000..3b5ceda1
--- /dev/null
+++ b/9-regular-expressions/14-regexp-lookahead-lookbehind/1-find-non-negative-integers/solution.md
@@ -0,0 +1,28 @@
+
+A number is `pattern:\d+`.
+
+We can exclude negatives by prepending it with the negative lookahead: `pattern:(?<!-)\d+`.
+
+If we try it now, we may notice one more "extra" result:
+
+```js run
+let reg = /(?<!-)\d+/g;
+
+let str = "0 12 -5 123 -18";
+
+console.log( str.match(reg) ); // 0, 12, 123, *!*8*/!*
+```
+
+It matches `match:8` of `subject:-18`. To exclude it, we need to ensure that the regexp starts matching a number not from the middle of another number.
+
+We can do it by specifying another negative lookbehind: `pattern:(?<!-)(?<!\d)\d+`. Now `pattern:(?<!\d)` ensures that a match does not start after another digit.
+
+Or we can use a single lookbehind here:
+
+```js run
+let reg = /(?<![-\d])\d+/g;
+
+let str = "0 12 -5 123 -18";
+
+alert( str.match(reg) ); // 0, 12, 123
+```
diff --git a/9-regular-expressions/14-regexp-lookahead-lookbehind/1-find-non-negative-integers/task.md b/9-regular-expressions/14-regexp-lookahead-lookbehind/1-find-non-negative-integers/task.md
new file mode 100644
index 00000000..1508d6d5
--- /dev/null
+++ b/9-regular-expressions/14-regexp-lookahead-lookbehind/1-find-non-negative-integers/task.md
@@ -0,0 +1,14 @@
+# Find non-negative integers
+
+There's a string of integer numbers.
+
+Create a regexp that looks for only non-negative ones (zero is allowed).
+
+An example of use:
+```js
+let reg = /your regexp/g;
+
+let str = "0 12 -5 123 -18";
+
+alert( str.match(reg) ); // 0, 12, 123
+```