ARST打卡第127周[127/521]

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class Solution {
public:
    int arrangeCoins(int n) {
        int left = 1, right = n;
        while (left < right) {
            int mid = (right - left + 1) / 2 + left;
            if ((long long) mid * (mid + 1) <= (long long) 2 * n) {
                left = mid;
            } else {
                right = mid - 1;
            }
        }
        return left;
    }
};

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class Solution {
public:
    int arrangeCoins(int n) {
        return (int) ((sqrt((long long) 8 * n + 1) - 1) / 2);
    }
};