合併排序
基本思想:遞歸分治法,將待排序的序列分成兩部分,然後對兩個部分進行排序,最終將排好序的子部分進行合併
public class hebing {
public static void main(String args[]){
int[] data = new int[] { 5, 3, 6, 2, 1, 9, 4, 8, 7 };
mergeSort(data,0,8);
for (int i = 0; i < data.length; i++) {
System.out.print(data[i] + "\t");
}
}
public static void mergeSort(int a[],int left,int right){
if(left<right){
int middle=(left+right)/2;
mergeSort(a,left,middle);
mergeSort(a,middle+1,right);
merge(a,left,middle,right);
}
}
public static void merge(int[] data, int left, int center, int right) {
// 創建一個臨時數組,將data數組分爲兩部分(兩部分已經排好序)left- center-1,center - right(排好序的兩部分),進行彙總
//彙總 ,data[left]與data[center],小者放入臨時數組第一位,然後將比較小的那部分後一位比較
int[] tmpArr = new int[data.length];
int mid = center + 1;
int third = left;
int tmp = left;
while (left <= center && mid <= right) {
if (data[left] <= data[mid]) {
tmpArr[third++] = data[left++];
} else {
tmpArr[third++] = data[mid++];
}
}
//兩部分中剩餘的部分放進臨時數組(實際只有一部分會有剩餘)
while (mid <= right) {
tmpArr[third++] = data[mid++];
}
while (left <= center) {
tmpArr[third++] = data[left++];
}
// 將臨時數組中的內容拷貝回原數組中
while (tmp <= right) {
data[tmp] = tmpArr[tmp++];
}
}
}