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46 lines
2.6 KiB
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46 lines
2.6 KiB
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<p>The hash of a <strong>0-indexed</strong> string <code>s</code> of length <code>k</code>, given integers <code>p</code> and <code>m</code>, is computed using the following function:</p>
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<ul>
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<li><code>hash(s, p, m) = (val(s[0]) * p<sup>0</sup> + val(s[1]) * p<sup>1</sup> + ... + val(s[k-1]) * p<sup>k-1</sup>) mod m</code>.</li>
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</ul>
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<p>Where <code>val(s[i])</code> represents the index of <code>s[i]</code> in the alphabet from <code>val('a') = 1</code> to <code>val('z') = 26</code>.</p>
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<p>You are given a string <code>s</code> and the integers <code>power</code>, <code>modulo</code>, <code>k</code>, and <code>hashValue.</code> Return <code>sub</code>,<em> the <strong>first</strong> <strong>substring</strong> of </em><code>s</code><em> of length </em><code>k</code><em> such that </em><code>hash(sub, power, modulo) == hashValue</code>.</p>
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<p>The test cases will be generated such that an answer always <strong>exists</strong>.</p>
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<p>A <b>substring</b> is a contiguous non-empty sequence of characters within a string.</p>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> s = "leetcode", power = 7, modulo = 20, k = 2, hashValue = 0
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<strong>Output:</strong> "ee"
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<strong>Explanation:</strong> The hash of "ee" can be computed to be hash("ee", 7, 20) = (5 * 1 + 5 * 7) mod 20 = 40 mod 20 = 0.
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"ee" is the first substring of length 2 with hashValue 0. Hence, we return "ee".
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</pre>
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<p><strong>Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> s = "fbxzaad", power = 31, modulo = 100, k = 3, hashValue = 32
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<strong>Output:</strong> "fbx"
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<strong>Explanation:</strong> The hash of "fbx" can be computed to be hash("fbx", 31, 100) = (6 * 1 + 2 * 31 + 24 * 31<sup>2</sup>) mod 100 = 23132 mod 100 = 32.
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The hash of "bxz" can be computed to be hash("bxz", 31, 100) = (2 * 1 + 24 * 31 + 26 * 31<sup>2</sup>) mod 100 = 25732 mod 100 = 32.
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"fbx" is the first substring of length 3 with hashValue 32. Hence, we return "fbx".
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Note that "bxz" also has a hash of 32 but it appears later than "fbx".
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 <= k <= s.length <= 2 * 10<sup>4</sup></code></li>
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<li><code>1 <= power, modulo <= 10<sup>9</sup></code></li>
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<li><code>0 <= hashValue < modulo</code></li>
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<li><code>s</code> consists of lowercase English letters only.</li>
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<li>The test cases are generated such that an answer always <strong>exists</strong>.</li>
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</ul>
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