查找算法

1）查找第N小的值
2）查找最小最大值

#!/usr/bin/env python3.3
# -*- coding:utf-8 -*-
# Copyright 2013

def randomized_select(data, n):
    if n > 0 and n <= len(data):
        left, right = 0, len(data) - 1
        pivot_index = partition(data, left, right)
        while pivot_index != n - 1: 
            if pivot_index < n - 1:
                left = pivot_index + 1
            else:
                right = pivot_index - 1
            pivot_index = partition(data, left, right)
        return data[pivot_index]

def min_max_select(data):
    if len(data) > 0:
        min_value = max_value = data[0]
        start_pos = 0 if len(data) % 2 == 0 else 1
        for i in range(start_pos, len(data)-1, 2):
            if data[i] < data[i+1]:
                if data[i] < min_value:
                    min_value = data[i]
                if data[i+1] > max_value:
                    max_value = data[i+1]
            else:
                if data[i+1] < min_value:
                    min_value = data[i+1]
                if data[i] > max_value:
                    max_value = data[i]
        return min_value, max_value