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46 lines
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46 lines
1.4 KiB
HTML
<p>Given an integer array <code>arr</code>, and an integer <code>target</code>, return the number of tuples <code>i, j, k</code> such that <code>i < j < k</code> and <code>arr[i] + arr[j] + arr[k] == target</code>.</p>
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<p>As the answer can be very large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</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> arr = [1,1,2,2,3,3,4,4,5,5], target = 8
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<strong>Output:</strong> 20
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<strong>Explanation: </strong>
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Enumerating by the values (arr[i], arr[j], arr[k]):
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(1, 2, 5) occurs 8 times;
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(1, 3, 4) occurs 8 times;
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(2, 2, 4) occurs 2 times;
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(2, 3, 3) occurs 2 times.
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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> arr = [1,1,2,2,2,2], target = 5
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<strong>Output:</strong> 12
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<strong>Explanation: </strong>
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arr[i] = 1, arr[j] = arr[k] = 2 occurs 12 times:
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We choose one 1 from [1,1] in 2 ways,
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and two 2s from [2,2,2,2] in 6 ways.
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</pre>
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<p><strong>Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> arr = [2,1,3], target = 6
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<strong>Output:</strong> 1
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<strong>Explanation:</strong> (1, 2, 3) occured one time in the array so we return 1.
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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>3 <= arr.length <= 3000</code></li>
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<li><code>0 <= arr[i] <= 100</code></li>
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<li><code>0 <= target <= 300</code></li>
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</ul>
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