【编程练习】快速排序，Java和Python实现

Java实现

public class QuickSort {

public static void sort(int[] a) {
sort(a, 0, a.length-1);
}

public static void sort(int[] a, int lo, int hi) {
if (lo >= hi) return;
int j = partition(a, lo, hi);
sort(a, lo, j - 1);
sort(a, j + 1, hi);
}

public static int partition(int[] a, int lo, int hi) {
int value = a[lo];
int i = lo;
int j = hi+1;
while (true) {
while (a[++i] <= value) {
if (i == hi){
break;
}
}
while (a[--j] >= value) {
if (j == lo){
break;
}
}
if (i>=j){
break;
}
exch(a, i, j);
}
exch(a,lo,j);
return j;
}
public static void exch(int[] a, int i, int j){
int temp = a[i];
a[i] = a[j];
a[j] = temp;
}
public static void main(String[] args) {
// 测试
int[] a = {3,7,5,2,4};
sort(a);
for (int i:a){
System.out.println(i);
}
}

}

Python实现

# -*- coding: utf-8 -*-

# 利用缺省参数实现函数重载
def sort(a, lo = None, hi = None):
if lo is None and hi is None:
sort(a, 0, len(a)-1)
return;
if lo is None or hi is None:
print 'error'
return;

if lo >= hi:
return;
j = partition(a, lo, hi)
sort(a, lo, j-1)
sort(a, j+1, hi)

# 切分
def partition(a, lo, hi):
value = a[lo]

while True:
i = lo + 1
j = hi
while a[i] <= value and i <= hi:
i += 1
while a[j] >= value and j > lo:
j -= 1
if i >= j:
break
a[i],a[j] = a[j], a[i]  # 交换两个元素的位置
a[lo], a[j] = a[j], a[lo]
return j

if __name__ == "__main__":
a = [3,7,5,2,4]
sort(a)
print a