题目介绍

解法

红蓝染色体法

java">class Solution {public long countFairPairs(int[] nums, int lower, int upper) {long res = 0;Arrays.sort(nums);for(int i = 0; i < nums.length -1; i++){int left = lowerBound(nums,lower - nums[i],i + 1); // >= lower-nums[i] 的位置int right = lowerBound(nums,upper - nums[i] + 1,i + 1) - 1; // <= upper-nums[j]的位置res = res + right - left + 1;}return res;}public int lowerBound(int[] nums, int target, int startidx) {int left = startidx, right = nums.length - 1; while (left <= right) { int mid = left + (right - left) / 2;if (nums[mid] < target) {left = mid + 1; } else {right = mid - 1; }}return left;}
}