二分查找及变种

基本的二分查找

public int binarySearch(int []a ,int key){
		int l = 0, h = a.length - 1, mid;
		int p = -1;
		while (l  <= h) {
			//System.out.println("l="+l+" h="+h);
			mid = (l + h) >> 1;
			if(key == a[mid]) return mid;
			if(key > a[mid]) l = mid + 1;
			else h = mid - 1;
		}
		return p;
	}

//有重复元素找到重复元素最大那个的index，找不到则找到上界限index
public int binarySearchLast(int []a ,int key){
		int l = 0, h = a.length - 1, mid;
		int p = -1;
		while (l  <= h) {
			mid = l + ((h-l) >> 1);
			if(key > a[mid] && mid + 1 < a.length && key < a[mid + 1]) return mid + 1;
			if(key >= a[mid]) {
				l = mid + 1;
				if(key == a[mid] && mid > p) p = mid;
			}
			else h = mid - 1;			
		}
		return p;
	}

参考：

http://blog.youkuaiyun.com/v_july_v/article/details/7093204