Java implementation of selection sort

---

Select sort Introduction

Principle:
each selection index of the current outer loop, the inner loop then, by determining, find the index of the position of the minimum or maximum; then exchanged on the two index values.

Improved bubble sort, from the number of exchanges O(N^2)is reduced to O(N), while the number of comparisons is O(N^2), in fact, equal to the maximum number of switching N-1 or

---

Select from the front backwards

Select rear front; each inner loop index minimum is found, switching to the front, the front orderly

public void sort1(int[] ary) {
    long startTime = System.nanoTime();

    int selectIndex;
    int len = ary.length;
    for (int i = 0; i < len; i++) {
        selectIndex = i;
        for (int j = i + 1; j < len; j++) {
            if (ary[selectIndex] > ary[j]) {
                selectIndex = j; //每轮内层循环得到最小值的 index
            }
            //如下则是得到大的 index
//                if (ary[j] > ary[selectIndex]) {
//                    selectIndex = j; //每轮内层循环得到最大值的 index
//                }
        }
        if (selectIndex != i) {
            Util.swap(ary, selectIndex, i);
        }
//            System.out.println(Arrays.toString(ary));
    }

    System.out.println("total time:" + ((System.nanoTime() - startTime) / 1.0e9));
}

---

Select from back to front

Selected from back; each inner loop index to find a maximum value, switching to the back, behind the orderly

public void sort2(int[] ary) {
   long startTime = System.nanoTime();

   int len = ary.length;
   int selectIndex;
   for (int i = len - 1; i >= 0; i--) {
       selectIndex = i;
       for (int j = i - 1; j >= 0; j--) {
           if (ary[selectIndex] < ary[j]) {
               selectIndex = j; //每轮内层循环得到最小值的 index
           }
       }
       if (selectIndex != i) {
           Util.swap(ary, selectIndex, i); //从后向前置换
       }
//            System.out.println(Arrays.toString(ary));
   }

   System.out.println("total time:" + ((System.nanoTime() - startTime) / 1.0e9));
}

Bubble sort performance (time consuming) Comparative

• Also completely reverse the order of the sequence
  significantly better bubble sort
• Fully random sequences
  better than most of the bubble sort implemented; realized slightly worse than the optimal bubble sort