寻找第k大数

/*************************************************************************    > File Name: k_fenshu.cpp    > Author: wangzhicheng    > Mail: [e-mail]    > Created Time: Sun 18 Jan 2015 10:47:12 PM WSTThis is a free program, you can modify or redistribute it under the term of GNU ************************************************************************/// search the k_th max number// for example, 3, 0, 1, 2, the 1 max number is 3, the 2 max number is 2#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <time.h>#include <iostream>#include <vector>#include <algorithm>using namespace std;/* * @purpose:partition a array, this is generally included in quick sort * */int partition(vector<int>&v, int start, int end) {int i, j;int k;int tmp;i = start;j = end;tmp = v[i];while(i < j) {while(i < j && v[j] > tmp) j--;if(i < j) v[i++] = v[j];while(i < j && v[i] < tmp) i++;if(i < j) v[j--] = v[i];}v[i] = tmp;return i;}void find_k_max(vector<int>&v, int start, int end, int k_th, int &k_max) {int pivot;int k;if(start <= end) {pivot = partition(v, start, end);k = end - pivot + 1;if(k == k_th) k_max = v[k];else if(k > k_th) find_k_max(v, pivot + 1, end, k_th, k_max);else find_k_max(v, start, pivot - 1, k_th - k, k_max);}}int main() { int n;int k_th, k_max;int i;cout << "number = ";cin >> n;cout << "k_th = ";cin >> k_th;if(k_th < 1 || k_th > n) {cerr << "imput error...!" << endl;exit(1);}vector<int>v(n);for(i = 0;i < n;i++) {cout << i << " = ";cin >> v[i];}find_k_max(v, 0, n - 1, k_th, k_max);cout << "k_max = " << k_max << endl;return 0;}