iOS用oc写几个常用的排序算法（选择排序，插入排序，快速排序）

用oc写了几个排序算法，没有特殊的修改，比较容易理解，给大家参考一下。

/*
 ***选择排序
*/
- (NSArray*)choose:(NSArray *)arr{
    if (arr.count < 2) {
        return nil;
    }
    if (arr.count == 2) {
        return nil;
    }
    NSMutableArray *muArr = [NSMutableArray arrayWithArray:arr];
    for (int i = 0; i < muArr.count - 1 ; i ++) {
        int temp = i + 1;
        for (int j = i + 1; j < muArr.count - 1; j ++) {
            if ([muArr[j + 1] intValue] <= [muArr[temp] intValue]) {
                temp = j + 1;
            }
        }
        if ([muArr[i] intValue] > [muArr[temp] intValue]) {
            NSString *tempStr = muArr[i];
            muArr[i] = muArr[temp];
            muArr[temp] = tempStr;
        }
    }
    return muArr;
}
/*
 ***插入排序
 */
- (NSArray*)insert:(NSArray*)arr{
    
    NSMutableArray *muArr = [NSMutableArray arrayWithArray:arr];
    
    for (int i = 0; i < arr.count; i ++) {
        for (int j = i - 1; j >= 0; j --) {
            
            if ([muArr[i] intValue] <= [muArr[j] intValue] && [muArr[i] intValue] >= [muArr[j - 1] intValue]) {
                NSString *tempStr = muArr[i];
                [muArr removeObjectAtIndex:i];
                [muArr insertObject:tempStr atIndex:j];
                break;
            }
        }
    }
    
    return muArr;
}

//快速排序
- (NSArray*)quick:(NSArray*)arr{
    if (arr.count == 1) {
        return arr;
    }
    if (arr.count == 2) {
        if ([arr[0] intValue] > [arr[1] intValue]) {
            return @[arr[1],arr[0]];
        }
        else{
            return arr;
        }
    }
    
    NSMutableArray *muArr1 = [NSMutableArray arrayWithArray:@[]];
    NSMutableArray *muArr2 = [NSMutableArray arrayWithArray:@[]];
    
    for (int i = 0; i < arr.count ; i ++) {
        if ([arr[i] intValue] <= [arr[arr.count / 2] intValue]) {
            [muArr1 addObject:arr[i]];
        }
        else {
            [muArr2 addObject:arr[i]];
        }
    }
    if (muArr1.count == arr.count) {
        [muArr2 addObject:arr[arr.count / 2]];
        [muArr1 removeObjectAtIndex:(arr.count / 2)];
    }
    else if (muArr2.count == arr.count){
        [muArr1 addObject:arr[arr.count / 2]];
        [muArr2 removeObjectAtIndex:(arr.count / 2)];
    }
    NSArray *arr1 = [self quick:muArr1];
    NSArray *arr2 = [self quick:muArr2];
    
    NSMutableArray *muarr = [NSMutableArray array];
    for (id temp in arr1) {
        [muarr addObject:temp];
    }
    for (id temp in arr2) {
        [muarr addObject:temp];
    }
    
    return muarr;
    
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    NSArray *frontArr = @[@"G",@"D",@"A",@"F",@"E",@"M",@"H",@"Z"];
    NSArray *midArr = @[@"A",@"D",@"E",@"F",@"G",@"H",@"M",@"Z"];
    NSLog(@"%@",[self sortTree:frontArr and:midArr]);
}
//前序遍历:G DAFE MHZ

//中序遍历：ADEF G HMZ

//                    G
//            D               M
//        A       F       H       Z
//              E
//后序遍历：AEFDHZMG

- (NSArray*)sortTree:(NSArray *)frontArr and:(NSArray*)midArr{
    if (frontArr.count != midArr.count || frontArr.count == 0) {
        return nil;
    }
    //拿到root节点。
    NSString *rootPoint = frontArr[0];
    //通过root节点和中序遍历结果，切割出中序遍历左右子树。（不含root节点）
    NSMutableArray *midLeftArr = [NSMutableArray array];
    NSMutableArray *midRightArr = [NSMutableArray array];
    int aNum = (int)[midArr indexOfObject:rootPoint];
    for (int i = 0; i < midArr.count ; i ++) {
        if (i < aNum) {
            [midLeftArr addObject:midArr[i]];
        }
        else if (i > aNum) {
            [midRightArr addObject:midArr[i]];
        }
    }
    //这里通过上面求出来左右子树的节点数，划分出前序遍历的左右子树。
    NSArray *frontLeftArr = [frontArr subarrayWithRange:NSMakeRange(1, midLeftArr.count)];
    NSArray *frontRightArr = [frontArr subarrayWithRange:NSMakeRange(1 + midLeftArr.count, midRightArr.count)];
    //递归求值，（把左右子树分别看作单独的二叉树进行递归）
    NSArray *lArr = [self sortTree:frontLeftArr and:midLeftArr];
    NSArray *rArr = [self sortTree:frontRightArr and:midRightArr];
    //我们知道了左子树和右子树还有节点，然后我们重新拼接一下就是我们需要的后序遍历了。
    NSMutableArray *sortArr = [NSMutableArray array];
    for (int i = 0; i < lArr.count; i ++) {
        [sortArr addObject:lArr[i]];
    }
    for (int i = 0; i < rArr.count; i ++) {
        [sortArr addObject:rArr[i]];
    }
    //别忘了root节点跟在最后面
    [sortArr addObject:rootPoint];
    //返回结果就是了
    return sortArr;
}