查找算法

二分查找

// 数组a必须是有序的
public static int get(int key, int[] a) {

	int lo = 0, hi = a.length - 1;
	while (lo <= hi) {
		int mid = lo + (hi - lo) / 2;
		if (key < a[mid]) {
			hi = mid - 1;
		}
		else if (key > a[mid]) {
			lo = mid + 1;
		}
		else {
			return mid;
		}
	}

	return -1;
}

二叉搜索树查找

class TreeNode {
	int val;
	TreeNode left;
	TreeNode right;

	TreeNode(int val) {
		this.val = val;
	}
}

public static get(TreeNode root, int val) {

	TreeNode node = null, cur = root;
	while (cur != null) {
		if (val > cur.val) {
			cur = cur.right;
		}
		else if (val < cur.val) {
			cur = cur.left;
		}
		else {
			node = cur;
			break;
		}
	}

	return node;
}