C++ 快排

// 进行一轮快排并返回当前的中间数
int getMiddle( int* arr, int low, int high ) {
    auto swaparr = [&]( int i, int j ) {
        int tmp = arr[i];
        arr[i] = arr[j];
        arr[j] = tmp;
    };

    if( high - low > 0 ) {
        int k = arr[low], i = low, j = high;
        while( i != j ) {
            //R->L
            for( ; j > i && arr[j] >= k; j-- );
            swaparr( i, j );
            //L->R
            for( ; i < j && arr[i] <= k; i++ );
            swaparr( i, j );
        }
        return i;
    }
    return -1;
}

//
void _fastSort( int* arr, int low, int high ) {
    int mid = getMiddle( arr, low, high );
    if( mid != -1 ) {
        _fastSort( arr, low, mid-1 );
        _fastSort( arr, mid+1, high );
    }
}
//
void fastSort(int* arr,int len) {
    if( arr && len )
        _fastSort( arr, 0, len -1 );
}