首先看两个有序数组的排序
public static int[] merge(int[] a, int[] b) {
int[] c = new int[a.length + b.length];
int i = 0, j = 0, l = 0;
while (i < a.length && j < b.length) {
c[l++] = a[i] <= b[j] ? a[i++] : b[j++];
}
while (i < a.length) {
c[l++] = a[i++];
}
while (j < b.length) {
c[l++] = b[j++];
}
return c;
}
归并算法：先拆分，直到只剩下一个值（本身为有序），再合并
public static void sort(int[] a,int low,int high) {
if(low==high)
return;
int mid = (low+high)/2;
if(low<high) {
sort(a, low, mid);
sort(a, mid+1, high);
merge(a, low,mid,high);
}
}
private static void merge(int[] a, int low, int mid, int high) {
int[] temp = new int[high-low+1];
int i = low;
int j = mid+1;
int k = 0;
while(i<=mid&&j<=high) {
temp[k++]=a[i]<=a[j]?a[i++]:a[j++];
}
while(i<=mid)
temp[k++]=a[i++];
while(j<=high)
temp[k++]=a[j++];
for(int x=0;x<temp.length;x++) {
a[x+low] = temp[x];
}
}
稳定性：稳定
时间复杂度：O(nlogn)
