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43 lines
1.2 KiB
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43 lines
1.2 KiB
HTML
<p>给你一个 <strong>下标从 0 开始</strong> 的整数数组 <code>nums</code> ，返回满足下述条件的 <strong>不同</strong> 四元组 <code>(a, b, c, d)</code> 的 <strong>数目</strong> ：</p>
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<ul>
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<li><code>nums[a] + nums[b] + nums[c] == nums[d]</code> ，且</li>
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<li><code>a < b < c < d</code></li>
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</ul>
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<p> </p>
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<p><strong>示例 1：</strong></p>
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<pre><strong>输入：</strong>nums = [1,2,3,6]
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<strong>输出：</strong>1
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<strong>解释：</strong>满足要求的唯一一个四元组是 (0, 1, 2, 3) 因为 1 + 2 + 3 == 6 。
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</pre>
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<p><strong>示例 2：</strong></p>
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<pre><strong>输入：</strong>nums = [3,3,6,4,5]
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<strong>输出：</strong>0
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<strong>解释：</strong>[3,3,6,4,5] 中不存在满足要求的四元组。
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</pre>
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<p><strong>示例 3：</strong></p>
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<pre><strong>输入：</strong>nums = [1,1,1,3,5]
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<strong>输出：</strong>4
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<strong>解释：</strong>满足要求的 4 个四元组如下：
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- (0, 1, 2, 3): 1 + 1 + 1 == 3
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- (0, 1, 3, 4): 1 + 1 + 3 == 5
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- (0, 2, 3, 4): 1 + 1 + 3 == 5
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- (1, 2, 3, 4): 1 + 1 + 3 == 5
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</pre>
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<p> </p>
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<p><strong>提示：</strong></p>
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<ul>
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<li><code>4 <= nums.length <= 50</code></li>
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<li><code>1 <= nums[i] <= 100</code></li>
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</ul>
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