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"title": "Longest Happy Prefix",
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"content": "<p>A string is called a <strong>happy prefix</strong> if is a <strong>non-empty</strong> prefix which is also a suffix (excluding itself).</p>\n\n<p>Given a string <code>s</code>, return <em>the <strong>longest happy prefix</strong> of</em> <code>s</code>. Return an empty string <code>""</code> if no such prefix exists.</p>\n\n<p> </p>\n<p><strong class=\"example\">Example 1:</strong></p>\n\n<pre>\n<strong>Input:</strong> s = "level"\n<strong>Output:</strong> "l"\n<strong>Explanation:</strong> s contains 4 prefix excluding itself ("l", "le", "lev", "leve"), and suffix ("l", "el", "vel", "evel"). The largest prefix which is also suffix is given by "l".\n</pre>\n\n<p><strong class=\"example\">Example 2:</strong></p>\n\n<pre>\n<strong>Input:</strong> s = "ababab"\n<strong>Output:</strong> "abab"\n<strong>Explanation:</strong> "abab" is the largest prefix which is also suffix. They can overlap in the original string.\n</pre>\n\n<p> </p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>1 <= s.length <= 10<sup>5</sup></code></li>\n\t<li><code>s</code> contains only lowercase English letters.</li>\n</ul>\n",
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