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package class47;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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// 利用只支持单点增加 + 范围查询的动态开点线段树（累加和），解决leetcode 315
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public class Problem_0315_CountOfSmallerNumbersAfterSelf {
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public static class Node {
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public int sum;
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public Node left;
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public Node right;
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}
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public static class DynamicSegmentTree {
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public Node root;
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public int size;
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public DynamicSegmentTree(int max) {
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root = new Node();
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size = max;
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}
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public void add(int i, int v) {
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add(root, 1, size, i, v);
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}
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private void add(Node c, int l, int r, int i, int v) {
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if (l == r) {
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c.sum += v;
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} else {
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int mid = (l + r) / 2;
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if (i <= mid) {
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if (c.left == null) {
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c.left = new Node();
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}
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add(c.left, l, mid, i, v);
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} else {
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if (c.right == null) {
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c.right = new Node();
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}
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add(c.right, mid + 1, r, i, v);
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}
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c.sum = (c.left != null ? c.left.sum : 0) + (c.right != null ? c.right.sum : 0);
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}
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}
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public int query(int s, int e) {
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return query(root, 1, size, s, e);
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}
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private int query(Node c, int l, int r, int s, int e) {
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if (c == null) {
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return 0;
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}
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if (s <= l && r <= e) {
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return c.sum;
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}
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int mid = (l + r) / 2;
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if (e <= mid) {
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return query(c.left, l, mid, s, e);
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} else if (s > mid) {
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return query(c.right, mid + 1, r, s, e);
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} else {
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return query(c.left, l, mid, s, e) + query(c.right, mid + 1, r, s, e);
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}
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}
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}
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public static List<Integer> countSmaller(int[] nums) {
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List<Integer> ans = new ArrayList<>();
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if (nums == null || nums.length == 0) {
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return ans;
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}
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int n = nums.length;
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for (int i = 0; i < n; i++) {
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ans.add(0);
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}
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int[][] arr = new int[n][];
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for (int i = 0; i < n; i++) {
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arr[i] = new int[] { nums[i], i };
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}
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Arrays.sort(arr, (a, b) -> (a[0] - b[0]));
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DynamicSegmentTree dst = new DynamicSegmentTree(n);
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for (int[] num : arr) {
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ans.set(num[1], dst.query(num[1] + 1, n));
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dst.add(num[1] + 1, 1);
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}
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return ans;
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}
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}
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