longest nondecreasing subsequence in O(nlgn)

Question

I have the following algorithm which works well

I tried explaining it here for myself http://nemo.la/?p=943 and it is explained here http://www.geeksforgeeks.org/lon

Answer 1

My Java version:

  public static int longestNondecreasingSubsequenceLength(List A) {
    int n = A.size();
    int dp[] = new int[n];
    int max = 0;
    for(int i = 0; i < n; i++) {
        int el = A.get(i);
        int idx = Arrays.binarySearch(dp, 0, max, el);
        if(idx < 0) {
            idx = -(idx + 1);
        }
        if(dp[idx] == el) { // duplicate found, let's find the last one 
            idx = Arrays.binarySearch(dp, 0, max, el + 1);
            if(idx < 0) {
                idx = -(idx + 1);
            }
        }
        dp[idx] = el;
        if(idx == max) {
            max++;
        }
    }
    return max;
}