排序算法详细过程：选择排序

demo地址：https://github.com/weiman152/PaiXu.git

选择排序是先比较，并不急着交换，而是记录最小的值的位置，把最小的值与第一个位置的值进行交换。然后第二轮的时候，再次遍历除了第一个位置的之外的其他数字，找出最小的，放在第二个位置。以此类推，最后得出排序后的数组。假如数组的个数为n，选择排序会进行 n+(n-1)+(n-2)+......+2+1次比较，最多进行n次交换。下面进行举例说明：（这里为了更加容易理解，把每一次的比较都列了出来）

qiaoba5.png

1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48

i: 第几轮比较
min: 当前最小值的下标
j: 同一轮中每一个值与最小值的比较

i=0://第一轮 min = 0 （步骤中用 m 代表）

j=1: 1(m), 16(), 23, 56, 89, 33, 7, 27, 55, 37, 48
j=2: 1(m), 16, 23(), 56, 89, 33, 7, 27, 55, 37, 48
j=3: 1(m), 16, 23, 56(), 89, 33, 7, 27, 55, 37, 48
j=4: 1(m), 16, 23, 56, 89(), 33, 7, 27, 55, 37, 48
j=5: 1(m), 16, 23, 56, 89, 33(), 7, 27, 55, 37, 48
j=6: 1(m), 16, 23, 56, 89, 33, 7(), 27, 55, 37, 48
j=7: 1(m), 16, 23, 56, 89, 33, 7, 27(), 55, 37, 48
j=8: 1(m), 16, 23, 56, 89, 33, 7, 27, 55(), 37, 48
j=9: 1(m), 16, 23, 56, 89, 33, 7, 27, 55, 37(), 48
j=10: 1(m), 16, 23, 56, 89, 33, 7, 27, 55, 37, 48()

第一轮比较完成结果：(找到最小值1，放到第一个位置,共比较了 n-1 次)

 结果：     1(m), 16, 23, 56, 89, 33, 7, 27, 55, 37, 48

i=1://第二轮 min = 1

j=2: 1(️), 16(m), 23(), 56, 89, 33, 7, 27, 55, 37, 48
j=3: 1(️), 16(m), 23, 56(), 89, 33, 7, 27, 55, 37, 48
j=4: 1(️), 16(m), 23, 56, 89(), 33, 7, 27, 55, 37, 48
j=5: 1(️), 16(m), 23, 56, 89, 33(), 7, 27, 55, 37, 48
j=6: 1(️), 16(m), 23, 56, 89, 33, 7(), 27, 55, 37, 48
j=7: 1(️), 16, 23, 56, 89, 33, 7(m), 27(), 55, 37, 48
j=8: 1(️), 16, 23, 56, 89, 33, 7(m), 27, 55(), 37, 48
j=9: 1(️), 16, 23, 56, 89, 33, 7(m), 27, 55, 37(), 48
j=10: 1(️), 16, 23, 56, 89, 33, 7(m), 27, 55, 37, 48()

比较完成之后交换 ：
     1(️), 7(m), 23, 56, 89, 33, 16, 27, 55, 37, 48

第二轮比较结果：

     1(️), 7(m), 23, 56, 89, 33, 16, 27, 55, 37, 48

i=2://第三轮 min = 2

 j=3:1(️), 7(️), 23(m), 56(), 89, 33, 16, 27, 55, 37, 48
 j=4:1(️), 7(️), 23(m), 56, 89(), 33, 16, 27, 55, 37, 48
 j=5:1(️), 7(️), 23(m), 56, 89, 33(), 16, 27, 55, 37, 48
 j=6:1(️), 7(️), 23(m), 56, 89, 33, 16(), 27, 55, 37, 48
 j=7:1(️), 7(️), 23, 56, 89, 33, 16(m), 27(), 55, 37, 48
 j=8:1(️), 7(️), 23, 56, 89, 33, 16(m), 27, 55(), 37, 48
 j=8:1(️), 7(️), 23, 56, 89, 33, 16(m), 27, 55, 37(), 48
 j=8:1(️), 7(️), 23, 56, 89, 33, 16(m), 27, 55, 37, 48()

 交换:1(️), 7(️), 16(m), 56, 89, 33, 23, 27, 55, 37, 48()

第三轮比较结果：

     1(️), 7(️), 16(m), 56, 89, 33, 23, 27, 55, 37, 48

i=3://第四轮 min = 3

j=4:1(️), 7(️), 16(️), 56(m), 89(), 33, 23, 27, 55, 37, 48
j=5:1(️), 7(️), 16(️), 56(m), 89, 33(), 23, 27, 55, 37, 48
j=6:1(️), 7(️), 16(️), 56, 89, 33, 23(), 27, 55, 37, 48
j=7:1(️), 7(️), 16(️), 56, 89, 33, 23(m), 27(), 55, 37, 48
j=8:1(️), 7(️), 16(️), 56, 89, 33, 23(m), 27, 55(), 37, 48
j=9:1(️), 7(️), 16(️), 56, 89, 33, 23(m), 27, 55, 37(), 48
j=10:1(️), 7(️), 16(️), 56, 89, 33, 23(m), 27, 55, 37, 48()

交换：1(️), 7(️), 16(️), 23(m), 89, 33, 56, 27, 55, 37, 48

第四轮比较结果：

1(️), 7(️), 16(️), 23(m), 89, 33, 56, 27, 55, 37, 48

.........

四轮比较下来，确认了前四个最小值。
下面我们就使用不同语言把代码写出来吧。

OC语言：

main函数：

#import <Foundation/Foundation.h>
#import "Sort.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
    
        //选择排序
        NSMutableArray * arr2= [NSMutableArray arrayWithArray:@[@1,@16,@23,@56,@89,@33,@7,@27,@55,@37,@48]];
        NSArray * select = [sort selectedSortWithArray:arr2];
        NSLog(@"选择：  %@",select);
        
    }
    return 0;
}

Sort类：

Sort.h：

#import <Foundation/Foundation.h>

@interface Sort : NSObject

/**
 选择排序

 @param array 排序前的数组
 @return 排序后的数组
 */
- (NSArray *)selectedSortWithArray:(NSMutableArray *)array;

Sort.m:

#import "Sort.h"

@implementation Sort

- (NSArray *)selectedSortWithArray:(NSMutableArray *)array {
    NSMutableArray * arr = [array mutableCopy];
    int min = 0;
    for (int j = 0; j<arr.count-1; j++) {
        min = j;//最小值下标记录
        for (int i = j+1; i<arr.count; i++) {
            if (arr[min] > arr[i]) {
                min = i;
            }
        }
        if (min!=j) {
            [arr exchangeObjectAtIndex:min withObjectAtIndex:j];
        }
        
    }
    
    return arr;
}


@end

Swift语言

main.swift

import Foundation

let mySort: Sort = Sort()
let arr2: [Int] = [1,16,23,56,89,33,7,27,55,37,48]
mySort.selectedSort(array: arr2)

Sort.swift

//
//  Sort.swift
//  Sort_Swift
//
//  Created by iOS on 2018/3/13.
//  Copyright © 2018年 weiman. All rights reserved.
//

import Cocoa

class Sort: NSObject {

    /// 选择排序
    ///
    /// - Parameter array: 需要排序的数组
    func selectedSort(array: [Int]) {
        var arr = array
        //记录最小值的下标
        var min = 0;
        for i in 0..<arr.count-1 {
            min = i
            for j in i+1..<arr.count {
                if arr[j] < arr[min] {
                    min = j
                }
            }
            if min != i {
                arr.swapAt(i, min)
            }
        }
        print("选择排序：    \(arr)")
    }
    
}

C语言

//
//  main.c
//  Sort_C
//
//  Created by iOS on 2018/3/13.
//  Copyright © 2018年 weiman. All rights reserved.
//

#include <stdio.h>

void selectedSort(int a[], int size);

int main(int argc, const char * argv[]) {
   
    printf("Hello, World!\n");
   
    int arr[] = {1,16,23,56,89,33,7,27,55,37,48};
    int sizeA = sizeof(arr)/sizeof(arr[0]);
    selectedSort(arr, sizeA);
    
    for(int i=0; i<sizeA; i++){
        printf(" %d ",arr[i]);
    }
    
    printf("\n");
    return 0;
}

/**
 选择排序

 @param a 排序的数组
 @param size 数组的长度
 */
void selectedSort(int a[], int size){
    
    int min = 0;
    for (int i = 0; i< size-1; i++) {
        min = i;
        for (int j=i+1; j<size; j++) {
            if (a[j]<a[min]) {
                min = j;
            }
        }
        if (min != i) {
            int tmp = a[i];
            a[i] = a[min];
            a[min] = tmp;
        }
    }
}

排序前： [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]

打印下排序执行的每一个步骤：

i:0,j:1 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:0,j:2 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:0,j:3 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:0,j:4 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:0,j:5 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:0,j:6 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:0,j:7 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:0,j:8 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:0,j:9 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:0,j:10 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:1,j:2 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:1,j:3 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:1,j:4 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:1,j:5 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:1,j:6 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:1,j:7 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:1,j:8 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:1,j:9 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:1,j:10 [1, 16, 23, 56, 89, 33, 7, 27, 55, 37, 48]
i:2,j:3 [1, 7, 23, 56, 89, 33, 16, 27, 55, 37, 48]
i:2,j:4 [1, 7, 23, 56, 89, 33, 16, 27, 55, 37, 48]
i:2,j:5 [1, 7, 23, 56, 89, 33, 16, 27, 55, 37, 48]
i:2,j:6 [1, 7, 23, 56, 89, 33, 16, 27, 55, 37, 48]
i:2,j:7 [1, 7, 23, 56, 89, 33, 16, 27, 55, 37, 48]
i:2,j:8 [1, 7, 23, 56, 89, 33, 16, 27, 55, 37, 48]
i:2,j:9 [1, 7, 23, 56, 89, 33, 16, 27, 55, 37, 48]
i:2,j:10 [1, 7, 23, 56, 89, 33, 16, 27, 55, 37, 48]
i:3,j:4 [1, 7, 16, 56, 89, 33, 23, 27, 55, 37, 48]
i:3,j:5 [1, 7, 16, 56, 89, 33, 23, 27, 55, 37, 48]
i:3,j:6 [1, 7, 16, 56, 89, 33, 23, 27, 55, 37, 48]
i:3,j:7 [1, 7, 16, 56, 89, 33, 23, 27, 55, 37, 48]
i:3,j:8 [1, 7, 16, 56, 89, 33, 23, 27, 55, 37, 48]
i:3,j:9 [1, 7, 16, 56, 89, 33, 23, 27, 55, 37, 48]
i:3,j:10 [1, 7, 16, 56, 89, 33, 23, 27, 55, 37, 48]
i:4,j:5 [1, 7, 16, 23, 89, 33, 56, 27, 55, 37, 48]
i:4,j:6 [1, 7, 16, 23, 89, 33, 56, 27, 55, 37, 48]
i:4,j:7 [1, 7, 16, 23, 89, 33, 56, 27, 55, 37, 48]
i:4,j:8 [1, 7, 16, 23, 89, 33, 56, 27, 55, 37, 48]
i:4,j:9 [1, 7, 16, 23, 89, 33, 56, 27, 55, 37, 48]
i:4,j:10 [1, 7, 16, 23, 89, 33, 56, 27, 55, 37, 48]
i:5,j:6 [1, 7, 16, 23, 27, 33, 56, 89, 55, 37, 48]
i:5,j:7 [1, 7, 16, 23, 27, 33, 56, 89, 55, 37, 48]
i:5,j:8 [1, 7, 16, 23, 27, 33, 56, 89, 55, 37, 48]
i:5,j:9 [1, 7, 16, 23, 27, 33, 56, 89, 55, 37, 48]
i:5,j:10 [1, 7, 16, 23, 27, 33, 56, 89, 55, 37, 48]
i:6,j:7 [1, 7, 16, 23, 27, 33, 56, 89, 55, 37, 48]
i:6,j:8 [1, 7, 16, 23, 27, 33, 56, 89, 55, 37, 48]
i:6,j:9 [1, 7, 16, 23, 27, 33, 56, 89, 55, 37, 48]
i:6,j:10 [1, 7, 16, 23, 27, 33, 56, 89, 55, 37, 48]
i:7,j:8 [1, 7, 16, 23, 27, 33, 37, 89, 55, 56, 48]
i:7,j:9 [1, 7, 16, 23, 27, 33, 37, 89, 55, 56, 48]
i:7,j:10 [1, 7, 16, 23, 27, 33, 37, 89, 55, 56, 48]
i:8,j:9 [1, 7, 16, 23, 27, 33, 37, 48, 55, 56, 89]
i:8,j:10 [1, 7, 16, 23, 27, 33, 37, 48, 55, 56, 89]
i:9,j:10 [1, 7, 16, 23, 27, 33, 37, 48, 55, 56, 89]

选择排序结果：
[1, 7, 16, 23, 27, 33, 37, 48, 55, 56, 89]