三分模板

凸函数的极大值

ll l, r;
while(l < r) {
    ll lmid = l + (r - l) / 3;
    ll rmid = r - (r - l) / 3;
    if(calc(lmid) <= calc(rmid))    l = lmid + 1;
    else r = rmid - 1;
}
printf("%lld\n", max(calc(l), calc(r)));

凹函数的极小值

ll l, r;
while(l < r) {
    ll lmid = l + (r - l) / 3;
    ll rmid = r - (r - l) / 3;
    if(calc(rmid) >= calc(lmid))    r = midr - 1;
    else     l = midl + 1;
}
printf("%lld\n", min(calc(l), calc(r)));

浮点数模板

凸函数的极大值

double l, r;
for(int i = 0; i < 300; i++) {
    double lmid = l + (r - l) / 3;
    double rmid = r - (r - l) / 3;
    if(calc(lmid) <= calc(rmid))    l = lmid;
    else     r = rmid;
}
printf("%.6f\n", calc(l));

凹函数的极小值

double l, r;
for(int i = 0; i < 300; i++) {
    double lmid = l + (r - l) / 3;
    double rmid = r - (r - l) / 3;
    if(calc(rmid) >= calc(lmid))    r = rmid;
    else     l = lmid;
}
printf("%.6f\n", calc(l));