g1901_2000.s1995_count_special_quadruplets.Solution Maven / Gradle / Ivy
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Java Solution for LeetCode algorithm problems, continually updating
package g1901_2000.s1995_count_special_quadruplets;
// #Easy #Array #Enumeration #2022_05_16_Time_2_ms_(99.20%)_Space_42.8_MB_(30.85%)
public class Solution {
public int countQuadruplets(int[] nums) {
int count = 0;
// max nums value is 100 so two elements sum can be max 200
int[] m = new int[201];
for (int i = 1; i < nums.length - 2; i++) {
for (int j = 0; j < i; j++) {
// update all possible 2 sums
m[nums[j] + nums[i]]++;
}
for (int j = i + 2; j < nums.length; j++) {
// fix third element and search for fourth - third in 2 sums as a + b + c = d == a
// + b = d - c
int diff = nums[j] - nums[i + 1];
if (diff >= 0) {
count += m[diff];
}
}
}
return count;
}
}