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class Solution {
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public:
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    int numberOfPoints(vector<vector<int>>& nums) {
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        int max_end = ranges::max(nums, {}, [](const auto& a) { return a[1]; })[1];
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        vector<int> diff(max_end + 2); // 注意下面有 end+1
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        for (auto& interval : nums) {
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            diff[interval[0]]++;
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            diff[interval[1] + 1]--;
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        }
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        int ans = 0, s = 0;
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        for (int d : diff) {
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            s += d;
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            ans += s > 0;
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        }
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        return ans;
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    }
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};