Benchmark Sections

• Test Data Generation
• Custom Fast Input
• Standard scanf()
• Default cin
• Optimized cin
• Results Summary

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Test Data Generator

#include <cstdio>
#include <cstdlib>
#include <windows.h>
#define reg register
using namespace std;

const int TOTAL_ENTRIES = 1919810;

int main() {
    freopen("test_input.txt", "w", stdout);
    srand(GetTickCount());
    for (reg int i = 0; i < TOTAL_ENTRIES; ++i) {
        printf("%d ", rand() - 16384);
    }
    return 0;
}

Custom Fast Integer Input

// Elapsed time for 1919810 integers: ~210ms
#include <cstdio>
#include <windows.h>
#define reg register
using namespace std;

const int TOTAL_ENTRIES = 1919810;

inline int fastIntRead() {
    reg int val = 0;
    reg int sign = 1;
    reg char c;
    while ((c = getchar()) && (c < '0' || c > '9')) {
        if (c == '-') sign = -1;
    }
    do {
        val = (val << 3) + (val << 1) + (c ^ 48);
    } while ((c = getchar()) && c >= '0' && c <= '9');
    return val * sign;
}

int main() {
    freopen("test_input.txt", "r", stdin);
    long start = GetTickCount();
    for (int i = 0; i < TOTAL_ENTRIES; ++i) {
        fastIntRead();
    }
    long end = GetTickCount();
    printf("%ld", end - start);
    return 0;
}

Standard scanf()

// Elapsed time for 1919810 integers: ~670ms
#include <cstdio>
#include <windows.h>
using namespace std;

const int TOTAL_ENTRIES = 1919810;

int main() {
    freopen("test_input.txt", "r", stdin);
    int tmp;
    long start = GetTickCount();
    for (int i = 0; i < TOTAL_ENTRIES; ++i) {
        scanf("%d", &tmp);
    }
    long end = GetTickCount();
    printf("%ld", end - start);
    return 0;
}

Default Unoptimized cin

// Elapsed time for 1919810 integers: ~1.3s (1300ms)
#include <iostream>
#include <cstdio>
#include <windows.h>
using namespace std;

const int TOTAL_ENTRIES = 1919810;

int main() {
    freopen("test_input.txt", "r", stdin);
    int tmp;
    long start = GetTickCount();
    for (int i = 0; i < TOTAL_ENTRIES; ++i) {
        cin >> tmp;
    }
    long end = GetTickCount();
    cout << (end - start) << endl;
    return 0;
}

cin with Synchronization Disabled

// Elapsed time for 1919810 integers: ~250ms
#include <iostream>
#include <cstdio>
#include <windows.h>
using namespace std;

const int TOTAL_ENTRIES = 1919810;

int main() {
    freopen("test_input.txt", "r", stdin);
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int tmp;
    long start = GetTickCount();
    for (int i = 0; i < TOTAL_ENTRIES; ++i) {
        cin >> tmp;
    }
    long end = GetTickCount();
    cout << (end - start) << endl;
    return 0;
}

Results Summary

• Custom fast input is slightly faster than optimized cin
• If you do not want to implement a custom fast read function, using cin with disabled synchronization offers excellent performence that is sufficeint for most competitiev programming use cases.