Bubble Sort

比较相邻两项，条件满足是就交换。

Bubble Sort.mp4

// declare an array of integers that are not sorted
int[] nums = { 5, 10, 3, 2, 4 };
// Output the unsorted array to the console
Console.WriteLine("Before: 5, 10, 3, 2, 4");
 // Use this to know when to stop the sorting routine
bool swapped;
// Here we use a do loop but could have used for or while loops as well.
do
{
    // set swapped to false so that we can ensure at least one pass on the array
    swapped = false;
    // This loop will iterate over the array from beginning to end
    for (int i = 0; i < nums.Length - 1; i++)
    {
        // here we use the i for the position in the array
        // So i is the first value to compare and i + 1 compares the adjacent value
        // Once i is incremented at the end of this loop, we compare the next two sets of values, etc.
        if (nums[i] > nums[i + 1])
        {
            // swap routine.  Could be a separate method as well but is used inline for simplicity here
            // temp is used to hold the right value in the comparison so we don't lose it.  That value will be replaced in the next step
            int temp = nums[i + 1];
            // Here we replace the right value with the larger value that was on the left.   See why we needed the temp variable above?
            nums[i + 1] = nums[i];
            // Now we assign the value that is in temp, the smaller value, to the location that was just vacated by the larger number
            nums[i] = temp;
            // Indicate that we did a swap, which means we need to continue to check the remaining values.
            swapped = true;
        }
    }
} while (swapped == true);
// output the sorted array to the console
Console.Write("After: ");
for (int i = 0; i < nums.Length; i++)
{
    Console.Write("{0}, ", nums[i]);
}
// Use Console.ReadLine() in the event application was started with debugging.
Console.ReadLine();

Insertion Sort

将当前未排序元素，插入到已排序列的恰当位置。

Insertion Sort.mp4

// Declare an integer array that is not sorted
int[] arr = { 7, 8, 4, 6, 2, 1 };
// Output the values of the array to the console
Console.WriteLine("Array before sort: 7,8,4,6,2,1");
// Declare variable for the insertion value
int newValue;
// The outer loop allows us to iterate over the complete array that we will use for sorting
for (var i = 1; i < arr.Length; i++)
{
    // set newValue equal to the second element in the array
    // we don't start at the first element because it has no preceding value
    // which means we can't move it any further forward in the array
    newValue = arr[i];
    // Also set the start of our inner loop to the same value as i
    var j = i;
    // This loop will check the value of j to ensure we have not reached the end of the iteration (j = 0)
    // but also checks to see if the value preceding the current value is larger.
    // If it is, we "swap" the value before this one, decrement j, and then test against the next value
    // This continues until we run out of numbers in the array (j = 0) or there are no more values larger than
    // the current number (newValue) to it's left (preceding it).
    while (j > 0 && arr[j - 1] > newValue)
    {
        arr[j] = arr[j - 1];
        j--;
    }
    arr[j] = newValue;
}
Console.Write("Array after sort: ");
foreach (var val in arr)
{
    Console.Write(val + ",");
}
Console.WriteLine();

Selection Sort

选出最大（小）的排出来。

Selection Sort.mp4

// Declare an integer array that is not sorted
int[] arr = { 7, 8, 4, 6, 2, 1 };
// Output the values of the array to the console
Console.WriteLine("Array before sort: 7,8,4,6,2,1");
//minPos will  keep track of where the minimum value is located
int minPos;
// outer loop will be responsible for ensuring we have iterated over the entire array
for (var i = 0; i < arr.Length - 1; i++)
{
    //set minPos to the current counter value for traversing the array
    minPos = i;
    // inner loop will perform the comparisons between the min and the other values in the array
    for (var j = i + 1; j < arr.Length; j++)
    {
        if (arr[j] < arr[minPos])
        {
            //minPos will keep track of the index that min is in, this is needed when a swap happens
            minPos = j;
        }
    }
    //if minPos no longer equals i, it indicates a smaller value existed so a swap must take place to sort the values
    if (minPos != i)
    {
        var temp = arr[i];
        arr[i] = arr[minPos];
        arr[minPos] = temp;
    }
}
Console.Write("Array after sort: ");
foreach (var val in arr)
{
    Console.Write(val + ",");
}
Console.WriteLine();