二分查找的几种不同的实现

来源：互联网发布：手机屏幕养兔子软件编辑：程序博客网时间：2024/06/06 11:42
不多说，直接上代码，注释解释清楚了
# include <iostream># include <vector># include <cstring># include <string># include <sstream># include <istream>using namespace std;////////////////////////////////////////////////////////////////////template <typename T>vector <T> scanf_r() {    cin.sync();    string input_string;    while(true) {        getline(cin, input_string);        if (input_string != "\n") break;    }    istringstream input_stream(input_string);    vector <T> ret;    T item;    while(input_stream >> item) ret.push_back(item);    return ret;}template <typename T>T scanf(string prompt="", istream & input_stream = cin){    T ret;    while (cout << prompt, !(input_stream >> ret)) {        input_stream.clear();  // reset the state of cin        input_stream.sync(); // synchronize the buffer of cin    }    return ret;}///////////////////////////////////////////////////////////////////////** * 最小的i， 满足arr[i] = target. 不存在 返回 -1 */int bin_1(vector<int> & arr, int target) {    int size = arr.size();    int l = 0, r = size - 1, mid;    while(l < r) {        mid = l + ((r - l) >> 1); // 奇数： 中间； 偶数： 两个中间数的第一个        if(arr[mid] < target)            l = mid + 1;        else // arr[i] >= target            r = mid;    }    return (arr[l] == target) ? l : -1;}/** * 最大i， 满足arr[i] = target。 不存在， 返回-1 */int bin_2(vector<int> & arr, int target) {    int size = arr.size();    int l = 0, r = size - 1, mid;    while(l < r) {        mid = l + ((r - l + 1) >> 1); // 奇数： 中间；  偶数 ： 两个中间数的第二个        if(arr[mid] > target)            r = mid - 1;        else // arr[i] <= target            l = mid;    }    return (arr[l] == target) ? l : -1;}/** * 求最小的i，使得a[i] > target，若不存在，则返回-1 */int bin_3(vector<int> & arr, int target) {    int size = arr.size();    int l = 0, r = size - 1, mid;    while(l < r) {        mid = l + ((r - l) >> 1);         if(arr[mid] > target)            r = mid;        else            l = mid + 1;    }    return (arr[l] > target) ? l : -1;}/** * 求最大的i，满足a[i] < target， 若不存在， 返回 -1 */int bin_4(vector<int> & arr, int target) {    int size = arr.size();    int l =0, r = size - 1, mid;    while(l < r) {        mid = l + ((r - l + 1) >> 1);        if(arr[mid] < target)            l = mid;        else            r = mid - 1;    }    return (arr[l] < target) ? l : -1;}/** * 求最小的i，满足a[i] >= target， 若不存在， 返回 -1 */int bin_5(vector<int> & arr, int target) {    int size = arr.size();    int l = 0, r = size - 1, mid;    while(l < r) {        mid = l + ((r - l) >> 1);        if(arr[mid] >= target)            r = mid;        else            l = mid + 1;    }    return (arr[l] >= target) ? l : -1;}/** * 求最大的i，满足a[i] <= target， 若不存在， 返回 -1 */int bin_6(vector<int> & arr, int target) {    int size = arr.size();    int l = 0, r = size - 1, mid;    while(l < r) {        mid = l + ((r - l + 1) >> 1);        if(arr[mid] <= target)            l = mid;        else            r = mid - 1;    }    return (arr[l] <= target) ? l : -1;}/////////////////////////////////////////////////////////////////////////////void test( int (*bin) ( vector<int> &, int), string title) {    cout << "------test " << title << " with target : 2 ----------" << endl;    for(int i = 0; i < 3; i++) {        vector<int> vec = scanf_r<int>();        cout << bin(vec, 2) << endl;    }    cout << "------- end ---------------" << endl;}////////////////////////////////////////////////////////////////////////////int main() {    bool is_on = true;    while(is_on) {        cout << "choose a bin function to test: ";        int key = scanf<int>();        switch(key) {            case 1:                test(bin_1, string("bin_1(min i  for arr[i] = target)"));                break;            case 2:                test(bin_2, string("bin_2(max i for arr[i] = target)"));                break;            case 3:                test(bin_3, string("bin_3(min i for arr[i] > target)"));                break;            case 4:                test(bin_4, string("bin_4(max i for arr[i] < target)"));                break;            case 5:                test(bin_5, string("bin_5(min i for arr[i] >= target)"));                break;            case 6:                test(bin_6, string("bin_6(max i for arr[i] <= target)"));                break;            case 0:                is_on = false;                break;            default:;        }    }    return 0;}
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