Binary search tree minimum sum from root to leaf

和bsf没有任何关系，leetcode相似题112，113，129，404的，简单。
113，backtracking

public class Solution {
    public int minPathSum(TreeNode root) {
        if(root == null) return 0;
        return helper(root);
    }
    public int helper(TreeNode root){
        if(root == null) return Integer.MAX_VALUE;
        if(root.left == null && root.right == null ) return root.val;
        return Math.min(helper(root.left),helper(root.right)) + root.val;
    }
}

257. Binary Tree Paths

public class Solution {
    public List binaryTreePaths(TreeNode root) {
        List res=new ArrayList<>();
        if(root==null) return res;
        dfs(res,"",root);
        return res;
    }
    public void dfs(List res,String s,TreeNode root){
        if(root.left==null&&root.right==null) res.add(s+root.val);
        if(root.left!=null) dfs(res,s+root.val+"->",root.left);
        if(root.right!=null) dfs(res,s+root.val+"->",root.right);
    }
}

112. Path Sum

public class Solution {
    public boolean hasPathSum(TreeNode root, int sum) {
        if(root==null) return false;
        if(root.left==null&&root.right==null) return sum==root.val;
        return hasPathSum(root.left,sum-root.val)||hasPathSum(root.right,sum-root.val);
    }
}

113. Path Sum II

public class Solution {
    public List> pathSum(TreeNode root, int sum) {
        List> res=new ArrayList<>();
        if(root==null) return res;
        dfs(root,sum,res,new ArrayList<>());
        return res;
    }
    public void dfs(TreeNode root,int sum,List> res,List list){
        list.add(root.val);
        if(root.left==null&&root.right==null&&sum==root.val){
            res.add(new ArrayList<>(list));
            list.remove(list.size()-1);
            return;
        }
        if(root.left!=null) dfs(root.left,sum-root.val,res,list);
        if(root.right!=null) dfs(root.right,sum-root.val,res,list);
        list.remove(list.size()-1);
    }
}

129. Sum Root to Leaf Numbers

public class Solution {
    public int sumNumbers(TreeNode root) {
        
        return sum(root,0);
    }
    public int sum(TreeNode root,int sum){
        if(root==null) return 0;
        if(root.left==null&&root.right==null) return root.val+sum*10;
        return sum(root.left,sum*10+root.val)+sum(root.right,sum*10+root.val);
    }
}

404. Sum of Left Leaves

public class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        if(root==null) return 0;
        int ans=0;
        if(root.left!=null){
            if(root.left.left==null&&root.left.right==null) ans+=root.left.val;
            else ans+=sumOfLeftLeaves(root.left);
        }
        if(root.right!=null){
            ans+=sumOfLeftLeaves(root.right);
        }
        return ans;
    }
}