1996. The Number of Weak Characters in the Game

Problem

You are playing a game that contains multiple characters, and each of the characters has two main properties: attack and defense. You are given a 2D integer array properties where properties[i] = [attacki, defensei] represents the properties of the ith character in the game.

A character is said to be weak if any other character has both attack and defense levels strictly greater than this character's attack and defense levels. More formally, a character i is said to be weak if there exists another character j where attackj > attacki and defensej > defensei.

Return **the number of *weak* characters**.

  Example 1:

Input: properties = [[5,5],[6,3],[3,6]]
Output: 0
Explanation: No character has strictly greater attack and defense than the other.

Example 2:

Input: properties = [[2,2],[3,3]]
Output: 1
Explanation: The first character is weak because the second character has a strictly greater attack and defense.

Example 3:

Input: properties = [[1,5],[10,4],[4,3]]
Output: 1
Explanation: The third character is weak because the second character has a strictly greater attack and defense.

  Constraints:

• 2 <= properties.length <= 10^5

• properties[i].length == 2

• 1 <= attacki, defensei <= 10^5

Solution (Java)

class Solution {
    public int numberOfWeakCharacters(int[][] properties) {
        Arrays.sort(properties, (a, b) -> a[0] == b[0] ? b[1] - a[1] : a[0] - b[0]);
        int max = properties[properties.length - 1][1];
        int count = 0;
        for (int i = properties.length - 2; i >= 0; i--) {
            if (properties[i][1] < max) {
                count++;
            }
            max = Math.max(max, properties[i][1]);
        }
        return count;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).