《翼星求生》新手生存攻略 怎麼獲得氧氣?
阿新 • • 發佈:2021-12-07
給你一個整數陣列 nums ,按要求返回一個新陣列counts 。陣列 counts 有該性質: counts[i] 的值是 nums[i] 右側小於nums[i] 的元素的數量。
來源:力扣(LeetCode)
連結:https://leetcode-cn.com/problems/count-of-smaller-numbers-after-self
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心之所向,素履以往 生如逆旅,一葦以航import java.util.ArrayList; import java.util.Collections; import java.util.List; class Solution { private int[] ans; /** * 當前 i 位置的數原來在 index[i] */ private int[] index; private int[] helper; private int[] indexHelper; private void mergeSort(int[] nums, int l, int r) { if (l >= r) { return; } int mid = (l + r) >> 1; mergeSort(nums, l, mid); mergeSort(nums, mid + 1, r); int p1 = l, p2 = mid + 1, p = l; while (p1 <= mid && p2 <= r) { if (nums[p1] <= nums[p2]) { indexHelper[p] = index[p2]; helper[p++] = nums[p2++]; } else { ans[index[p1]] += (r - p2 + 1); indexHelper[p] = index[p1]; helper[p++] = nums[p1++]; } } while (p1 <= mid) { indexHelper[p] = index[p1]; helper[p++] = nums[p1++]; } while (p2 <= r) { indexHelper[p] = index[p2]; helper[p++] = nums[p2++]; } for (int i = l; i <= r; ++i) { index[i] = indexHelper[i]; } System.arraycopy(helper, l, nums, l, r - l + 1); } public List<Integer> countSmaller(int[] nums) { if (nums == null || nums.length == 0) { return Collections.emptyList(); } this.ans = new int[nums.length]; this.index = new int[nums.length]; this.helper = new int[nums.length]; this.indexHelper = new int[nums.length]; for (int i = 0; i < nums.length; ++i) { index[i] = i; } int[] copy = new int[nums.length]; System.arraycopy(nums, 0, copy, 0, nums.length); mergeSort(copy, 0, nums.length - 1); List<Integer> ret = new ArrayList<>(ans.length); for (int i = 0; i < ans.length; ++i) { ret.add(ans[i]); } return ret; } }