题解 | #查找#

#include <iostream>
#include <cstdio>
#include <algorithm>

using namespace std;

const int MAX_NUM = 100;

/**
 * 线性查找
 * @param arr
 * @param n
 * @param target
 * @return
 */
int linearSearch(int arr[], int n, int target) {
    for (int i = 0; i < n; ++i) {
        if (arr[i] == target) {
            return i;
        }
    }
    return -1;
}

/**
 * 二分查找
 * @param arr
 * @param n
 * @param target
 * @return
 */
int binarySearch(int arr[], int n, int target) {
    int left = 0;
    int right = n - 1;
    while (left <= right) {
        /*
         * 若mid = (left+right)/2 当left和right接近整形最大值时可能溢出
         * 下面的写法效果相同且不会有溢出问题
         */
        int mid = left + ((right - left) >> 1);
        if (target < arr[mid]) {
            right = mid - 1;
        } else if (target > arr[mid]) {
            left = mid + 1;
        } else {
            return mid;
        }
    }
    return -1;
}

/**
 * 查找--北京邮电大学
 * @return
 */
int main() {
    int numArr[MAX_NUM];
    int n;
    cin >> n;
    for (int i = 0; i < n; ++i) {
        cin >> numArr[i];
    }
    /*
     * 二分查找之前要先排序
     */
    sort(numArr, numArr + n);

    int m;
    cin >> m;
    int target;
    for (int j = 0; j < m; ++j) {
        cin >> target;
        if (binarySearch(numArr, n, target) != -1) {
            cout << "YES" << endl;
        } else {
            cout << "NO" << endl;
        }
    }

    return 0;
}