Given a 0-indexed integer array nums, return the number of distinct quadruplets (a, b, c, d) such that:
nums[a] + nums[b] + nums[c] == nums[d], anda < b < c < d
Example 1:
Input: nums = [1,2,3,6] Output: 1 Explanation: The only quadruplet that satisfies the requirement is (0, 1, 2, 3) because 1 + 2 + 3 == 6.
Example 2:
Input: nums = [3,3,6,4,5] Output: 0 Explanation: There are no such quadruplets in [3,3,6,4,5].
Example 3:
Input: nums = [1,1,1,3,5] Output: 4 Explanation: The 4 quadruplets that satisfy the requirement are: - (0, 1, 2, 3): 1 + 1 + 1 == 3 - (0, 1, 3, 4): 1 + 1 + 3 == 5 - (0, 2, 3, 4): 1 + 1 + 3 == 5 - (1, 2, 3, 4): 1 + 1 + 3 == 5
Constraints:
4 <= nums.length <= 501 <= nums[i] <= 100struct Solution;
impl Solution {
fn count_quadruplets(nums: Vec<i32>) -> i32 {
let n = nums.len();
let mut res = 0;
for i in 0..n {
for j in i + 1..n {
for k in j + 1..n {
for l in k + 1..n {
if nums[i] + nums[j] + nums[k] == nums[l] {
res += 1;
}
}
}
}
}
res
}
}
#[test]
fn test() {
let nums = vec![1, 2, 3, 6];
let res = 1;
assert_eq!(Solution::count_quadruplets(nums), res);
let nums = vec![3, 3, 6, 4, 5];
let res = 0;
assert_eq!(Solution::count_quadruplets(nums), res);
let nums = vec![1, 1, 1, 3, 5];
let res = 4;
assert_eq!(Solution::count_quadruplets(nums), res);
}