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把 100 拆分成 4 个正整数之和，有多少种拆分方法（无序）？
source link: https://www.zhihu.com/question/288336997/answer/1726745631
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把 100 拆分成 4 个正整数之和，有多少种拆分方法（无序）？
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使用C++20的ranges来做。
#include <iostream>
#include <range/v3/all.hpp>
using namespace ranges;
int main(int argc, char** argv) {
auto ints = views::iota(1, 101);
auto result =
count_if(
views::cartesian_product(ints, ints, ints, ints),
[](auto p) {
auto [x, y, z, t] = p;
return (x <= y && y <= z && z <= t
&& x + y + z + t == 100);
});
std::cout << result << std::endl; // 7153
return 0;
}
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