如何求数对之差的最大值

package java程序员面试笔试宝典;

public class 题8_5_11求数对之差的最大值 {
	//二分查找法没有做，感觉很复杂
	public static void main(String[] args) {
		int[] a={1,4,17,3,2,9};
		//System.out.println(getMax(a));
		//getMax_0(a);
		getMax1(a);
		
	}
	public static void getMax0(int[] a){
		if(a==null||a.length<=1){
			return ;
		}
		int max=a[0];
		int min=a[1];
		int result=max-min;
		for (int i = 2; i < a.length; i++) {
			max=max(max, a[i-1]);
			min=min(min, a[i]);
			result=max-min;
		}
		System.out.println(result);
		
		
	}
	public static void getMax1(int[] a){
		int min=a[a.length-1];
		int max=a[a.length-2];
		int result=max-min;
		for (int i = a.length-3; i >=0; i--) {
			max=max(max, a[i]);
			min=min(min, a[i+1]);
			result=max-min;
		}
		System.out.println(result);
	}
	
	
	//动态规划,每次变化减数
	public static int getMax_0(int[] a){
		if(a==null||a.length<2){
			return Integer.MIN_VALUE;
		}
		int max=Integer.MIN_VALUE;
		int maxRes=Integer.MIN_VALUE;
		for (int i = 0; i+1< a.length; i++) {
			max=max(max, a[i]);
			maxRes=max(max-a[i+1], maxRes);
		}
		System.out.println(maxRes);
		return 0;
	}
	//动态规划,每次变化被减数
	public static int getMax_1(int[] a){
		if(a==null||a.length<2){
			return Integer.MIN_VALUE;
		}
		int minNum=Integer.MAX_VALUE;
		int maxRes=Integer.MIN_VALUE;
		for (int i = a.length-1; i>=0; i--) {
			maxRes=max(a[i]-minNum, maxRes);
			minNum=min(minNum, a[i]);
		}
		System.out.println(maxRes);
		return maxRes;
	}
	public static int max(int a,int b){
		return a>b?a:b;
	}
	public static int min(int a,int b){
		return a>b?b:a;
	}
	//蛮力法
	public static int getMax(int[] a){
		int max=a[0]-a[1];
		for (int i = 0; i < a.length; i++) {
			for (int j = i+1; j < a.length; j++) {
				if(a[i]-a[j]>max){
					max=a[i]-a[j];
				}
			}
		}
		System.out.println(max);
		return max;
	}
}