算法

模板：

 

// 二分
class Solution {
public:
    /**
     * @param nums: An integer array sorted in ascending order
     * @param target: An integer
     * @return: An integer
     */
    int findPosition(vector<int> &nums, int target) {
        // write your code here
        
        if(nums.size() == 0)    return -1;
        
        int start = 0;
        int end = nums.size()-1;
        int mid;
        
        while(start+1 < end)
        {
            mid = start + (end - start)/2;
            if(nums[mid] == target)
                return mid;
            else if(nums[mid] > target)
                end = mid;
            else if(nums[mid] < target)
                start = mid;
        }
        
        if(nums[start] == target)
            return start;
        if(nums[end] == target)
            return end;
        
        return -1;
    }
};

　　

// 二叉树前序遍历

public List<Integer> preorderTraversal(TreeNode root)
{ 
    Stack<TreeNode> stack = new Stack<TreeNode>();
    List<Integer> preorder = new ArrayList<Integer>();

    if(root == null) return preorder;

    stack.push(root);

    while(!stack.empty())
    {
      TreeNode node = stack.pop();
      preorder.add(node.val);
      if(node.right != null)
        stack.push(node.right);
      if(node.left != null)
        stack.push(node.left);
    }
    return preorder;
}