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 <= 105properties[i].length == 21 <= attacki, defensei <= 105