Problem Link: https://www.codechef.com/LTIME36/problems/ASTRING This problem can be solved using a segment tree RMQ. But I'm thinking of an alternative greedy approach which isn't working. I'm getting constant WA.

The idea is : since we need to take a substring of length k we need to perform (n — k) remove operations. So I'm removing the largest character in the string starting from the minimum index and this is supposed to ensure the lexicographically smallest substring. This approach gets WA. Anyone with bug in my approach or any counter example will be appreciated. Thanks.

Segment tree code : http://pastebin.com/gkx44cTP

My greedy code : http://pastebin.com/gEV1chkC