// DFS-Java
class Solution {public List<List<Integer>> res = new LinkedList<>();public List<List<Integer>> levelOrder(TreeNode root) {dfs(0, root);return res;}private void dfs(int level, TreeNode root){if(root == null) return;if(res.size() <= level){res.add(new LinkedList<>());}res.get(level).add(root.val);dfs(level+1, root.left);dfs(level+1, root.right);}
}

// BFS-Java
class Solution {public List<List<Integer>> levelOrder(TreeNode root) {List<List<Integer>> res = new LinkedList<>();Queue<TreeNode> queue = new LinkedList<>();if(root == null) return res;queue.add(root);while(!queue.isEmpty()){int level = queue.size();List<Integer> tempList = new LinkedList<>();for(int i = 0; i < level; i++){if(queue.peek().left != null) queue.add(queue.peek().left);if(queue.peek().right != null) queue.add(queue.peek().right);tempList.add(queue.poll().val);}res.add(tempList);}return res;}
}

// 二分查找
class Solution {public int mySqrt(int x) {if(x == 0 || x == 1) return x;long left = 1, right = x, mid = 1;while(left <= right){mid = left + (right - left) / 2;if(mid * mid > x){right = mid - 1;} else {left = mid + 1;}}return (int) right;}
}

// 牛顿迭代法
class Solution {public int mySqrt(int x) {long r = x;while (r * r > x) {r = (r + x / r) / 2;}return (int)r;}
}

// 倒序贪心
class Solution {public boolean canJump(int[] nums) {if (nums == null) return false;int endReachable = nums.length - 1;for (int i = nums.length - 1; i >= 0; i--){if(nums[i] + i >= endReachable){endReachable = i;}}return endReachable == 0;}
}

// 正序贪心
class Solution {public boolean canJump(int[] nums) {int maxPos = 0;for (int i = 0; i < nums.length; i++){if(i > maxLen) return false;maxPos = Math.max(maxPos, nums[i] + i);if(maxPos >= nums.length-1) break;}return true;}
}