lintcode：整数排序||

题目

给一组整数，按照升序排序。使用归并排序，快速排序，堆排序或者任何其他 O(n log n) 的排序算法。

解题

归并排序

public class Solution {
    /**
     * @param A an integer array
     * @return void
     */
    public void sortIntegers2(int[] A) {
        // Write your code here
        if(A==null || A.length <=1)
            return;
        int low = 0;
        int high = A.length - 1;
        mergeSort(A,low,high);

    }
    public void mergeSort(int[] A,int low ,int high){
        if(low>=high)
            return;
        int mid = low + (high - low)/2;
        mergeSort(A,low,mid);
        mergeSort(A,mid+1,high);
        merge(A,low,mid,high);

    }
    public void merge(int[] A,int low,int mid,int high){
        int len = high - low + 1;
        int[] C = new int[len];
        int i = low;
        int j = mid + 1;
        int k = 0;
        while(i<=mid && j<= high){
            if(A[i]>A[j]){
                C[k++] = A[j];
                j++;
            }else{
                C[k++] = A[i];
                i++;
            }
        }
        while(i<=mid){
            C[k++] = A[i];
            i++;
        }
        while(j<=high){
            C[k++] = A[j];
            j++;
        }
        for(k=0;k<len;k++){
            A[low+k] = C[k];
        }
    }
}