leecode 307 线段树

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package LeeCode;

public class LeetCode307 {

    private Tree tree;

    public LeetCode307(int[] nums) {
        tree = new Tree(nums);
    }

    public void update(int i, int val) {
        tree.update(i, val);
    }

    public int sumRange(int i, int j) {
        return tree.sumRange(i, j);
    }

    public static class Node{
        private int left;
        private int right;
        private int sum;
        private Node leftChild;
        private Node rightChild;
        private Node parent;

        public Node(){}

        public Node(int left, int right, int sum){
            this.left = left;
            this.right = right;
            this.sum = sum;
            parent = null;
        }
    }

    public static class Tree {
        private Node root;
        private int[] nums;
        private int[] sums;

        public Tree(int[] nums) {
            if(nums == null || nums.length == 0){
                return;
            }
            sums = new int[nums.length];
            sums[0] = nums[0];
            for (int i = 1; i < nums.length; i++) {
                sums[i] = sums[i - 1] + nums[i];
            }
            root = new Node(0, nums.length - 1, sums[nums.length - 1]);
            build(root, 0, nums.length - 1);
        }

        private void build(Node node, int left, int right) {
            if (left >= right) {
                return;
            }

            int middle = (left + right) / 2;
            Node leftChild = new Node(left, middle, left == 0 ?
                    sums[middle] : sums[middle] - sums[left - 1]);
            leftChild.parent = node;
            Node rightChild = new Node(middle + 1, right, sums[right] - sums[middle]);
            rightChild.parent = node;

            node.leftChild = leftChild;
            node.rightChild = rightChild;
            build(leftChild, left, middle);
            build(rightChild, middle + 1, right);
        }

        public int sumRange(int left, int right) {
            return sumRange(root, left, right);
        }

        public int sumRange(Node node, int left, int right) {
            if (left == node.left && right == node.right) {
                return node.sum;
            }
            int middle = (node.left + node.right) / 2;
            if (right <= middle) {
                return sumRange(node.leftChild, left, right);
            } else {
                if (left >= middle + 1) {
                    return sumRange(node.rightChild, left, right);
                } else {
                    return sumRange(node.leftChild, left, middle) +
                            sumRange(node.rightChild, middle + 1, right);
                }
            }
        }

        public void update(int index, int value) {
            Node curNode = root;
            while (true) {
                if (curNode.left == index && curNode.right == index) {
                    curNode.sum = value;
                    break;
                }
                int middle = (curNode.left + curNode.right) / 2;
                if (index <= middle) {
                    curNode = curNode.leftChild;
                } else {
                    curNode = curNode.rightChild;
                }
            }

            curNode = curNode.parent;
            while (curNode != null){
                curNode.sum = (curNode.leftChild == null ? 0 : curNode.leftChild.sum) +
                        (curNode.rightChild == null ? 0 : curNode.rightChild.sum);
                curNode = curNode.parent;
            }
        }

    }

    public static void main(String[] args) {
        int nums[] = {1,3,5};
        LeetCode307 leetCode307 = new LeetCode307(nums);
        System.out.println(leetCode307.sumRange(0, 2));
        leetCode307.update(1,2);
        System.out.println(leetCode307.sumRange(0, 2));
    }

}

leecode 307 线段树

标签：e30   rgs   str   value   break   tree   lse   amp   vat   

原文地址：https://www.cnblogs.com/wanggeEzio/p/13543341.html