Solution.java

class Trie {
    private Trie[] children = new Trie[2];

    public Trie() {
    }

    public void insert(int x) {
        Trie node = this;
        for (int i = 30; i >= 0; --i) {
            int v = x >> i & 1;
            if (node.children[v] == null) {
                node.children[v] = new Trie();
            }
            node = node.children[v];
        }
    }

    public int search(int x) {
        Trie node = this;
        int ans = 0;
        for (int i = 30; i >= 0; --i) {
            int v = x >> i & 1;
            if (node.children[v ^ 1] != null) {
                ans |= 1 << i;
                node = node.children[v ^ 1];
            } else {
                node = node.children[v];
            }
        }
        return ans;
    }
}

class Solution {
    public int findMaximumXOR(int[] nums) {
        Trie trie = new Trie();
        int ans = 0;
        for (int x : nums) {
            trie.insert(x);
            ans = Math.max(ans, trie.search(x));
        }
        return ans;
    }
}