0354. Russian Doll Envelopes
https://leetcode.com/problems/russian-doll-envelopes
Description
You are given a 2D array of integers envelopes
where envelopes[i] = [wi, hi]
represents the width and the height of an envelope.
One envelope can fit into another if and only if both the width and height of one envelope are greater than the other envelope's width and height.
Return the maximum number of envelopes you can Russian doll (i.e., put one inside the other).
Note: You cannot rotate an envelope.
Example 1:
**Input:** envelopes = [[5,4],[6,4],[6,7],[2,3]]
**Output:** 3
**Explanation:** The maximum number of envelopes you can Russian doll is 3 ([2,3] => [5,4] => [6,7]).
Example 2:
**Input:** envelopes = [[1,1],[1,1],[1,1]]
**Output:** 1
Constraints:
1 <= envelopes.length <= 5000
envelopes[i].length == 2
1 <= wi, hi <= 104
ac
class Solution {
public int maxEnvelopes(int[][] envelopes) {
// 1) sort array, width asc / height desc
Arrays.sort(envelopes, (a, b) -> {return a[0] != b[0] ? a[0] - b[0] : b[1] - a[1];});
// 2) only look at height, it's LIS now, use binary search to solve it.
int n = envelopes.length;
int[] dp = new int[n];
int len = 0;
for (int[] e : envelopes) {
int l = 0, r = len;
while (l < r) {
int mid = l + (r - l) / 2;
if (dp[mid] < e[1]) l = mid + 1;
else r = mid;
}
dp[l] = e[1];
if (l == len) len++;
}
return len;
}
}
/*
conver to LIS problem. 1) sort array, width asc / height desc, because [6,4] can't fit in [6,7], so can't appear before it, otherwise it will count 1 in LIS problem. 2) only look at height, it's LIS now, use binary search to solve it.
*/
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