# 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].

``````class Solution {
public:
int findLongestChain(vector<vector<int>>& pairs) {
stack<vector<int>> st;
sort(pairs.begin(), pairs.end(), [](vector<int>& a, vector<int>& b) {
return a[1] < b[1];
});
for (auto pair : pairs) {
if (st.empty()) st.push(pair);
else {
auto t = st.top();
if (pair[0] > t[1]) st.push(pair);
}
}
return st.size();
}
};
``````

``````class Solution {
public:
int findLongestChain(vector<vector<int>>& pairs) {
int res = 0, end = INT_MIN;
sort(pairs.begin(), pairs.end(), [](vector<int>& a, vector<int>& b) {
return a[1] < b[1];
});
for (auto pair : pairs) {
if (pair[0] > end) {
++res;
end = pair[1];
}
}
return res;
}
};
``````

Increasing Subsequences

Longest Increasing Subsequence

Non-overlapping Intervals