问题收集1

算法部分

1.快速排序

/**
 快速排序
 */
-(void)quickSort:(NSMutableArray *)arr {
    NSInteger left = 0;
    NSInteger right = arr.count - 1;
    while (left < right) {
        while (left < right && arr[left] <= arr[right]) {
            [arr exchangeObjectAtIndex:left withObjectAtIndex:right];
            right --;
        }
        while (left < right && arr[left] > arr[right]) {
            [arr exchangeObjectAtIndex:left withObjectAtIndex:right];
            left ++;
        }
    }
}
 /// 快排
    /// - Parameter arr: 要排序的数组
    func kuaipai(arr: inout [Int],left: Int,right: Int) {
        if left > right {
            return
        }
        var i = left
        var j = right
        let key = arr[i]
        while i < j {
            while (i < j && key <= arr[j]) {
                j = j - 1
            }
            while (i < j && key >= arr[i]) {
                i = i + 1
            }
            if (i < j) {
                let t = arr[i]
                arr[i] = arr[j]
                arr[j] = t
            }
        }
        arr[left] = arr[i]
        arr[i] = key
        kuaipai(arr: &arr, left: left, right: i - 1)
        kuaipai(arr: &arr, left: i + 1, right: right)
    }

2.冒泡排序

/**
 冒泡排序
 */
- (void)bubbleSort:(NSMutableArray *)arrM {
    for (NSInteger i = 0; i < arrM.count; i ++) {
        for (NSInteger j = 0; j < arrM.count - 1 - i;  j++) {
            if ([arrM[j] integerValue] < [arrM[j + 1] integerValue]) {
                [arrM exchangeObjectAtIndex:j withObjectAtIndex:j + 1];
            }
        }
    }
}

3.希尔排序

 希尔排序
 */
- (void)shellSort:(NSMutableArray *)arr{
    
    NSInteger gap = arr.count / 2;//1
    while (gap > 0) {
        for (NSInteger i = gap; i < arr.count; i ++) {
            NSInteger j = i;
            while (j - gap >= 0 && [arr[j] integerValue] < [arr[j - gap]  integerValue]) {
                [arr exchangeObjectAtIndex:j withObjectAtIndex:j - gap];
                j -= gap;
            }
  

        }
        gap = gap / 2;
    }
}

4.插入排序

/**
 插入排序
 */
- (void)insertionSort:(NSMutableArray *)arr {
    for (NSInteger i = 1; i < arr.count; i ++) {
        NSInteger temp = [[arr objectAtIndex:i] integerValue];
        NSInteger j = i;
        while (j > 0 && temp < [[arr objectAtIndex:j-1] integerValue]) {
            [arr replaceObjectAtIndex:j withObject:[arr objectAtIndex:j-1]];
            j--;
        }

        [arr replaceObjectAtIndex:j withObject:[NSNumber numberWithInt:temp]];
    }
    NSLog(@"%@",arr);
}

5.统计出现的字符串

/**
 统计出现的字符串

 */
- (void)lettersCount:(NSString *)str {
    NSMutableDictionary *dic = [NSMutableDictionary dictionary];
    for (NSInteger i = 0; i < str.length; i ++) {
        NSString *key = [NSString stringWithFormat:@"%c",[str characterAtIndex:i]];
        if (![dic.allKeys containsObject:key]) {
            dic[key] = @1;
        }else {
            NSInteger value = [dic[key] integerValue];
            value ++;
            dic[key] = [NSNumber numberWithInteger:value];
        }
        
    }
    NSLog(@"%@",dic);
}

6.push pop

/**
 题目：我现在需要实现一个栈，这个栈除了可以进行普通的push、pop操作以外，还可以进行getMin的操作，getMin方法被调用后，会返回当前栈的最小值，你会怎么做呢？你可以假设栈里面存的都是int整数
 */
- (void)push:(NSInteger)data {
   
    [self.dataArr addObject:@(data)];
    if (self.dataArr.count > 1) {
        if (data < [self.dataArr[self.dataArr.count - 2] integerValue]) {
            [self.minsArr addObject:@(self.dataArr.count - 1)];
        }
    }else {
        [self.minsArr addObject:@0];
    }
}
- (void)pop {
    if (self.dataArr.count > 0) {
        if ([self.dataArr.lastObject integerValue] != [self.dataArr[self.minsArr.count - 1] integerValue]) {
            [self.minsArr removeLastObject];
        }
        [self.dataArr removeLastObject];
//        return [self.dataArr.lastObject integerValue];
    }
    ////最好抛出异常 -1可能是push的
//    return -19574;
}
- (NSInteger)getMin {
    if (self.dataArr.count > 0) {
        NSInteger index = [[self.minsArr lastObject] integerValue];
        return [self.dataArr[index] integerValue];
    }
    //同上
    return -19574;
}