力扣878.第N个神奇数字

• 二分答案

  • check()：公共部分为最大公倍数的倍数

•   class Solution {const long MOD = 1e9 + 7;public:int nthMagicalNumber(int n, int a, int b) {//lcm函数 求最大公倍数long lcm = std::lcm(a,b);auto check = [&](long long mid) -> bool{long long res = mid / a + mid / b - mid / lcm;if(res >= n) return true;return false;};long long l = 0,r = (long long)min(a,b)*n;while(l<r){long long mid = l + r >> 1;if(check(mid)) r = mid;else l = mid + 1;}return l%MOD;}};