“四方定理”是数论中著名的一个定理，指所有自然数至多只要用四个数的平方和就可以表示。
- #include <iostream>
- using namespace std;
-
- int main() {
- long n, a, b, c, d;
- cout << "请输入一个数：" << endl;
- cin >> n;
- for (a = 1; a <= n; a++) {
- for (b = 1; b <= a; b++) {
- for (c = 1; c <= b; c++) {
- for (d = 1; d <= c; d++) {
- if ((a * a + b * b + c * c + d * d) == n) {
- cout << a << "*" << a << "+" << b << "*" << b << "+" << c << "*" << c << "+" << d << "*" << d << "=" << n <<endl;
- break;
- }
- }
- }
- }
- }
- }
-
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