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L315.java
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L315.java
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package Algorithm;
import java.util.Arrays;
import java.util.List;
public class L315 {
class Node{
int val;
int sum; //从数组的最后到当前访问节点时,在当前节点左边,且小于当前节点的个数,这个下面会解释。
int dup; //此val的个数 [1,1,2,3] ,1的dup为2,2的dup为1, 默认为1
Node left;
Node right;
public Node(int val, int sum) {
this.val = val;
this.sum = sum;
this.dup = 1;
}
}
public List<Integer> countSmaller(int[] nums) {
Node root = null;
Integer [] arr = new Integer[nums.length];
for(int i = nums.length - 1; i >= 0; i --) {
root = helper(root, nums[i], i, arr, 0);
}
return (List<Integer>) Arrays.asList(arr);
}
public Node helper(Node root, int num, int i, Integer [] arr, int preSum) {
if(root == null) {
root = new Node(num, 0);
arr[i] = preSum;
}else if (root.val == num) {
root.dup ++;
arr[i] = preSum + root.sum;
}else if (root.val < num) {
root.right = helper(root.right, num, i, arr, root.dup + root.sum + preSum);
}else {
root.sum ++;
root.left = helper(root.left, num, i, arr, preSum);
}
return root;
}
}