关于数组的算法

package algorithm;
/**
 * 
 * @author hasee
 *
 */
public class RotageOrderPrint {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[][] arr= new int[][] {
			{1,2,3,4,5},
			{6,7,8,9,10},
			{11,12,13,14,15},
			{16,17,18,19,20},
			{21,22,23,24,25}
		};
		rotag(arr);
	}
	
	public static void rotag(int[][] arr) {
		int a = 0;
		int b = 0;
		int c = arr.length - 1;
		int d = arr[0].length - 1;
		while(a<c) {
			rotaEdge(arr,a++,b++,c--,d--);
		}
		rotaPrint(arr);
		
	}

	private static void rotaPrint(int[][] arr) {
		// TODO Auto-generated method stub
		for(int i = 0;i < arr.length;i++) {
			for(int j = 0;j < arr[0].length;j++) {
				System.out.print(arr[i][j]+" ");
			}
			System.out.println();
		}
	}

	public static void rotaEdge(int[][] arr, int a, int b, int c, int d) {
		// TODO Auto-generated method stub
		int times = c - a;
		int tmp = 0;
		for(int i = 0;i < times;i++) {
			tmp = arr[a][b+i];
			arr[a][b+i] = arr[c-i][b];
			arr[c-i][b] = arr[c][d-i];
			arr[c][d-i] = arr[a+i][d];
			arr[a+i][d] = tmp;
		}
		
	}
	
	

}

package algorithm;
/**
 * 循环打印一个数组
 * @author hasee
 *
 */
public class sprialOrderPrint {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[][] arr = new int[][] {{1,2,3,4},
								   {5,6,7,8},
								   {9,10,11,12},
								   {13,14,15,16},
								   {17,18,19,20}
		
		};
		sqrialOrder(arr);
	}
	
	
	public static void sqrialOrder(int[][] arr) {
		int LB = 0;
		int LE = 0;
		int RB = arr.length-1;
		int RE = arr[0].length-1;
		while(LB<=RB && LE<=RE) {
			sqlrialPrint(arr,LB++,LE++,RB--,RE--);
		}
	}


	private static void sqlrialPrint(int[][] arr, int lb, int le, int rb, int re) {
		// TODO Auto-generated method stub
		if(lb == rb) {
			for(int i = le;i <= re;i++) {
				System.out.print(arr[lb][i]+" ");
			}
		}else if(le == re) {
			for(int i = lb;i<=rb;i++) {
				System.out.print(arr[i][le]+" ");
			}
		}else {
			int a =lb;
			int b =le;
			while(b < re) {
				System.out.print(arr[lb][b++]+" ");
			}
			while(a < rb)
				System.out.print(arr[a++][re]+" ");
			while(b > le)
				System.out.print(arr[rb][b--]+" ");
			while(a > lb)
				System.out.print(arr[a--][le]+" ");
		}
	}

}

package algorithm;
/**
 * 给定一个数组，和一个数num，把小于num的书放在数组左边，大于num的书放在数组右边
 *
 */
public class test4 {


	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[] a = {5,1,4,3,6,3,8,4,6,5};
		convert(a,5);
		for (int i : a) {
			System.out.println(i);
		}
	}
	
	
	public static void convert(int[]a ,int num) {
		int l = -1;
		int r = a.length;
		int cur = 0;
		while(cur<r) {
			if(a[cur]<num) {
				swap(a,++l,cur++);
			}else if(a[cur]>num) {
				swap(a,--r,cur);
			}else {
				cur++;
			}
		}
		
	}




	private static void swap(int[] a, int l, int cur) {
		// TODO Auto-generated method stub
		int temp = a[l];
		a[l] = a[cur];
		a[cur] = temp;
	}


}

package algorithm;

/**
 * 使用归并算法求小和问题
 * @author hasee
 *
 */
public class smallSum {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[] a = {1,2,3,4,5,6,1};
		System.out.println(merge(a));
	}
	public static int merge(int[] a) {
		if(a==null || a.length<2)
			return 0;
		return mergeSort(a,0,a.length-1);
	}
	private static int mergeSort(int[] a, int l, int r) {
		// TODO Auto-generated method stub
		if (l == r)
	        return 0;
	    int mid = l + (r - l) / 2;
	    return mergeSort(a, l, mid) + mergeSort(a, mid + 1, r) + merge(a, l, mid, r);
	}
	private static int merge(int[] a, int l, int mid, int r) {
		// TODO Auto-generated method stub
		 int count = 0;
		    int p1 = l;
		    int p2 = mid + 1;
		    int i = 0;
		    int[] help = new int[r-l+1];
		    while (p1 <= mid && p2 <= r)
		    {
		        count += a[p1] < a[p2] ? (r - p2 + 1)*a[p1] : 0;
		        help[i++] = a[p1] < a[p2] ? a[p1++] : a[p2++];
		    }
		   
		    return count;
	}
	

}