regexp task

9-regular-expressions/14-regexp-lookahead-lookbehind/1-find-non-negative-integers/solution.md

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+
+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
+```

9-regular-expressions/14-regexp-lookahead-lookbehind/1-find-non-negative-integers/task.md

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+# 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
+```