'commit'

TangDou/CSP-J/J2-2021/AcWing1221_ErFen_2.cpp

@@ -0,0 +1,54 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+const int N = 5e6 + 10;
+
+struct Node {
+    int c, d, sum;
+    bool operator<(const Node &t) const {
+        if (sum != t.sum) return sum < t.sum;
+        if (c != t.c) return c < t.c;
+        return d < t.d;
+    }
+} f[N];
+
+int n;
+int idx;
+
+int main() {
+    scanf("%d", &n);
+
+    // C预处理出 c^2+d^2
+    for (int c = 0; c * c <= n; c++)
+        for (int d = c; c * c + d * d <= n; d++)
+            f[idx++] = {c, d, c * c + d * d};
+
+    //结构体排序
+    sort(f, f + idx);
+
+    //枚举a^2+b^2
+    for (int a = 0; a * a <= n; a++) {
+        for (int b = a; a * a + b * b <= n; b++) {
+            int t = n - a * a - b * b;
+
+            //手写二分模板,左闭右开
+            // STL二分缺点:
+            // 1、常数较大,速度慢
+            // 2、对于结构体二分，需要构造空的Struct,还需要有一些玄学的赋零操作，不推荐
+            //结论：全面采用手写二分办法，忘记STL的二分写法
+            int l = 0, r = idx;
+            while (l < r) {
+                int mid = (l + r) >> 1;
+                if (f[mid].sum >= t)
+                    r = mid;
+                else
+                    l = mid + 1;
+            }
+            if (f[l].sum == t) {
+                cout << a << ' ' << b << ' ' << f[l].c << ' ' << f[l].d << ' ' << endl;
+                exit(0);
+            }
+        }
+    }
+    return 0;
+}