646. Maximum Length of Pair Chain

You are given `n` pairs of numbers. In every pair, the first number is always smaller than the second number.

Now, we define a pair `(c, d)` can follow another pair `(a, b)` if and only if `b < c`. Chain of pairs can be formed in this fashion.

Given a set of pairs, find the length longest chain which can be formed. You needn't use up all the given pairs. You can select pairs in any order.

Example 1:

```Input: [[1,2], [2,3], [3,4]]
Output: 2
Explanation: The longest chain is [1,2] -> [3,4]
```

Note:

1. The number of given pairs will be in the range [1, 1000].

646. Maximum Length of Pair Chain
``````struct Solution;

impl Solution {
fn find_longest_chain(mut pairs: Vec<Vec<i32>>) -> i32 {
let n = pairs.len();
pairs.sort_by_key(|p| p[1]);
let mut res = 0;
let mut cur = std::i32::MIN;
for i in 0..n {
if cur < pairs[i][0] {
cur = pairs[i][1];
res += 1;
}
}
res as i32
}
}

#[test]
fn test() {
let pairs = vec_vec_i32![[1, 2], [2, 3], [3, 4]];
let res = 2;
assert_eq!(Solution::find_longest_chain(pairs), res);
}
``````