31 lines
837 B
Markdown
31 lines
837 B
Markdown
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Given an integer array `arr`, and an integer `target`, return the number of tuples `i, j, k` such that `i < j < k` and `arr[i] + arr[j] + arr[k] == target`.
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As the answer can be very large, return it **modulo** `109 + 7`.
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**Example 1:**
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Input: arr = [1,1,2,2,3,3,4,4,5,5], target = 8
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Output: 20
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Explanation:
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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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**Example 2:**
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Input: arr = [1,1,2,2,2,2], target = 5
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Output: 12
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Explanation:
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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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**Constraints:**
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* `3 <= arr.length <= 3000`
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* `0 <= arr[i] <= 100`
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* `0 <= target <= 300`
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