g2301_2400.s2364_count_number_of_bad_pairs.Solution Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of leetcode-in-java21 Show documentation

Java-based LeetCode algorithm problem solutions, regularly updated

There is a newer version: 1.38

package g2301_2400.s2364_count_number_of_bad_pairs;

// #Medium #Array #Hash_Table #2022_08_14_Time_44_ms_(80.00%)_Space_55.3_MB_(100.00%)

import java.util.HashMap;

/**
 * 2364 - Count Number of Bad Pairs\.
 *
 * Medium
 *
 * You are given a **0-indexed** integer array `nums`. A pair of indices `(i, j)` is a **bad pair** if `i < j` and `j - i != nums[j] - nums[i]`.
 *
 * Return _the total number of **bad pairs** in_ `nums`.
 *
 * **Example 1:**
 *
 * **Input:** nums = [4,1,3,3]
 *
 * **Output:** 5
 *
 * **Explanation:** 
 *
 * The pair (0, 1) is a bad pair since 1 - 0 != 1 - 4.
 *
 * The pair (0, 2) is a bad pair since 2 - 0 != 3 - 4, 2 != -1. 
 *
 * The pair (0, 3) is a bad pair since 3 - 0 != 3 - 4, 3 != -1. 
 *
 * The pair (1, 2) is a bad pair since 2 - 1 != 3 - 1, 1 != 2. 
 *
 * The pair (2, 3) is a bad pair since 3 - 2 != 3 - 3, 1 != 0. 
 *
 * There are a total of 5 bad pairs, so we return 5.
 *
 * **Example 2:**
 *
 * **Input:** nums = [1,2,3,4,5]
 *
 * **Output:** 0
 *
 * **Explanation:** There are no bad pairs.
 *
 * **Constraints:**
 *
 * *   1 <= nums.length <= 10⁵
 * *   1 <= nums[i] <= 10⁹
**/
public class Solution {
    public long countBadPairs(int[] nums) {
        HashMap seen = new HashMap<>();
        long count = 0;
        for (int i = 0; i < nums.length; i++) {
            int diff = i - nums[i];
            if (seen.containsKey(diff)) {
                count += (i - seen.get(diff));
            } else {
                count += i;
            }
            seen.put(diff, seen.getOrDefault(diff, 0) + 1);
        }
        return count;
    }
}