# Same DP solution, Why use Collections.sort is faster than Arrays.sort

• Collections sort 300 ms

``````public class Solution {

private class ArrayComparator implements Comparator<int[]> {
@Override
public int compare(int[] a, int[] b) {
return a[0] - b[0];
}
}

public int maxEnvelopes(int[][] envelopes) {
if (envelopes == null || envelopes.length == 0) return 0;
List<int[]> list = new ArrayList<>();
for (int[] env : envelopes) list.add(env);
Collections.sort(list, new ArrayComparator());
int[] dp = new int[list.size()];
int res = 0;
Arrays.fill(dp, 1);
for (int i = 0; i < list.size(); i++) {
for (int j = 0; j < i; j++) {
if (list.get(i)[0] > list.get(j)[0] && list.get(i)[1] > list.get(j)[1]) {
dp[i] = Math.max(dp[i], 1 + dp[j]);
}
}
res = Math.max(res, dp[i]);
}
return res;
}
}
``````

Use Arrays.sort need 600ms

``````public class Solution {

private class ArrayComparator implements Comparator<int[]> {
@Override
public int compare(int[] a, int[] b) {
return a[0] - b[0];
}
}

public int maxEnvelopes(int[][] envelopes) {
if (envelopes == null || envelopes.length == 0) return 0;
int n = envelopes.length, res = 0;
Arrays.sort(envelopes, new ArrayComparator());
int[] dp = new int[n];
Arrays.fill(dp, 1);
for (int i = 0; i < n; i++) {
for (int j = 0; j < i; j++) {
if (envelopes[i][0] > envelopes[j][0] && envelopes[i][1] > envelopes[j][1]) {
dp[i] = Math.max(dp[i], 1 + dp[j]);
}
}
res = Math.max(res, dp[i]);
}
return res;
}
}``````

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