洛谷 P1571 眼红的Medusa

/*第一种，就是写二分函数
因为要按照a数组的顺序输出，那么则把b数组排序之后进行二分查找
若a中该元素存在b数组，则输出即可
*/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int binary_search(int* a, int x, int left, int right);//二分查找
int cmp(const void* a, const void* b);//快排的cmp函数

int a[100001] = { 0 }, b[100001] = { 0 };

int main(void) {
    int n, m;

    scanf("%d %d", &n, &m);
    for (int i = 0; i < n; i++) scanf("%d", &a[i]);
    for (int i = 0; i < m; i++)    scanf("%d", &b[i]);
    qsort(b, m, sizeof(int), cmp);

    int flag = 0;//空格处理
    for (int i = 0; i < n; i++) {
        if (binary_search(b, a[i], 0, m - 1)) {
            if (!flag) { printf("%d", a[i]); flag = 1; }
            else printf(" %d", a[i]);
        }    
    }

    return 0;
}

int cmp(const void* a, const void* b) {
    return *(int*)a - *(int*)b;
}

int binary_search(int* a, int x, int left, int right) {
    int mid;
    while (left <= right) {
        mid = (right + left) >> 1;// 除二
        if (a[mid] == x) return 1;
        else if (a[mid] > x)    right = mid - 1;
        else left = mid + 1;
    }
    return 0;
}

/*第二中，用C++ STL中的Binary search，存在返回真，否则假
因为要按照a数组的顺序输出，那么则把b数组排序之后进行二分查找
若a中该元素存在b数组，则输出即可
*/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<algorithm>
using namespace std;

int cmp(const void* a, const void* b);//快排的cmp函数

int a[100001] = { 0 }, b[100001] = { 0 };

int main(void) {
    int n, m;

    scanf("%d %d", &n, &m);
    for (int i = 0; i < n; i++) scanf("%d", &a[i]);
    for (int i = 0; i < m; i++)    scanf("%d", &b[i]);
    qsort(b, m, sizeof(int), cmp);

    int flag = 0;//空格处理
    for (int i = 0; i < n; i++) {
        if (binary_search(b, b + m, a[i])) {
            if (!flag) { printf("%d", a[i]); flag = 1; }
            else printf(" %d", a[i]);
        }    
    }

    return 0;
}

int cmp(const void* a, const void* b) {
    return *(int*)a - *(int*)b;
}