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938. Range Sum of BST

本文主要是介绍938. Range Sum of BST,对大家解决编程问题具有一定的参考价值,需要的程序猿们随着小编来一起学习吧!

Although this is an easy question, but it is prone to bugs, and the code can be better.

Following is my first solution, didn't use the feature of BST.

private int sum =0;
    public int rangeSumBST(TreeNode root, int low, int high) {
        if(root==null)
            return sum;
        if(root.val>=low&&root.val<=high){
            sum+=root.val;
        }
        rangeSumBST(root.left, low, high);    //whether root.val is in the range or not, this line should be executed, think about why
        rangeSumBST(root.right, low, high);   //whether root.val is in the range or not, this line should be executed, think about why
return sum; }

The following solution use the feature of BST, reduced unnecessary implementations:

    private int sum =0;
    public int rangeSumBST(TreeNode root, int low, int high) {
        if(root==null)
            return sum;
        if(root.val>high)
            rangeSumBST(root.left, low, high);
        else if(root.val<low)
            rangeSumBST(root.right, low, high);
        else{
            sum+=root.val;
            rangeSumBST(root.left, low, high);
            rangeSumBST(root.right, low, high);
        }
        return sum;
    }

The sum in above solution can be removed:

    public int rangeSumBST(TreeNode root, int low, int high) {
        if (root == null)
            return 0;
        if (root.val > high)
            return rangeSumBST(root.left, low, high);
        else if (root.val < low)
            return rangeSumBST(root.right, low, high);
        else {
            return rangeSumBST(root.left, low, high) + rangeSumBST(root.right, low, high) + root.val;
        }
    }

 

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