整數三分/浮點三分模板

轉自https://www.cnblogs.com/lukelmouse/p/12545973.html

• 整數三分模板

int l = 1,r = 100;
while(l < r) {
    int lmid = l + (r - l) / 3;
    int rmid = r - (r - l) / 3;
    lans = f(lmid),rans = f(rmid);
    // 求凹函數的極小值
    if(lans <= rans) r = rmid - 1;
    else l = lmid + 1;
    // 求凸函數的極大值
    if(lasn >= rans) l = lmid + 1;
    else r = rmid - 1;
}
// 求凹函數的極小值
cout << min(lans,rans) << endl;
// 求凸函數的極大值
cout << max(lans,rans) << endl;

• 浮點三分模板

const double EPS = 1e-9;
while(r - l < EPS) {
    double lmid = l + (r - l) / 3;
    double rmid = r - (r - l) / 3;
    lans = f(lmid),rans = f(rmid);
    // 求凹函數的極小值
    if(lans <= rans) r = rmid;
    else l = lmid;
    // 求凸函數的極大值
    if(lans >= rans) l = lmid;
    else r = rmid;
}
// 輸出 l 或 r 都可
cout << l << endl;