还是std::min好哇
by 星小雨 @ 2019-03-05 15:03:20
邪教！自带maxmin慢出翔，手写if()大法好
by ArachnidaQueen @ 2019-03-05 15:05:50
自带maxmin开氧也不慢啊qaqaq
by Juan_feng @ 2019-03-05 15:07:36
@[ArachnidaQueen](/space/show?uid=157671) 我就想知道库函数也是if实现的，怎么就比你的if慢了？
by SeKong @ 2019-03-05 15:08:04
@[Skqliao](/space/show?uid=38018) inline
by ⚡GG⚡ @ 2019-03-05 15:11:47
@[垃圾一个](/space/show?uid=85933) 看过源代码再说吧，库函数一样inline了。
by SeKong @ 2019-03-05 15:16:59
@[Skqliao](/space/show?uid=38018) 说得好像我不想知道似的……自己测过，每1e9次，max/min是if(a>/<b)的2.0-2.2倍：）
by ArachnidaQueen @ 2019-03-05 15:17:46
c++用bits，pascal用math啊
by shuiyuhan @ 2019-03-05 15:22:42
主要是min/max应该还封装了别的。。所以比较慢
by 星小雨 @ 2019-03-05 15:27:12
@[ArachnidaQueen](/space/show?uid=157671)
```
#include <bits/stdc++.h>
#include <sys/time.h>
const int MAXN = 1e5 + 5;
int A[MAXN];
int N = 3e4;
struct timeval timeStart, timeEnd, timeSystemStart;
inline int min(int x, int y) { return x < y ? x : y; }
void solve1() {
gettimeofday(&timeSystemStart, NULL);
int res = 0;
for (int i = 1; i <= N; ++i) {
for (int j = 1; j <= N; ++j) {
if (std::min(A[i], A[j]) == A[i])
++res;
}
}
gettimeofday(&timeEnd, NULL);
double runTime = (timeEnd.tv_sec - timeStart.tv_sec) +
(double)(timeEnd.tv_usec - timeStart.tv_usec) / 1000000;
printf("runTime is %lf\n", runTime);
}
void solve2() {
gettimeofday(&timeSystemStart, NULL);
int res = 0;
for (int i = 1; i <= N; ++i) {
for (int j = 1; j <= N; ++j) {
if (min(A[i], A[j]) == A[i])
++res;
}
}
gettimeofday(&timeEnd, NULL);
double runTime = (timeEnd.tv_sec - timeStart.tv_sec) +
(double)(timeEnd.tv_usec - timeStart.tv_usec) / 1000000;
printf("runTime is %lf\n", runTime);
}
int main() {
srand((unsigned long long)(new char));
for (int i = 1; i <= N; ++i) {
A[i] = rand();
}
solve1();
solve2();
return 0;
}
```
```
runTime is 1551770656.728527
runTime is 1551770665.015233
runTime is 1551770679.403779
runTime is 1551770687.715325
runTime is 1551770697.452731
runTime is 1551770705.809634
runTime is 1551770715.237783
runTime is 1551770723.584966
runTime is 1551770742.322617
runTime is 1551770750.776139
```
没开O2，请问你2倍的时间从何而来？能从原理上解释一下同样是一个if判断，为什么你的就能比他快一倍？
by SeKong @ 2019-03-05 15:31:14