Optimize the cost of concatenation of all these strings into one big string.

You have n strings with their lengths. You are given an add(string s1,string s2) which would concatenate the string s2 with s1 and return s3. Optimize the cost of concatenation of all these strings into one big string.
Eg: 1,5,2 are the lengths of given strings.
1+5=6
6+2=8
total cost=14 can you Optimize this total cost?

Source : Sent by a reader named rahul.

Print the objects of an array in the order of decreasing frequency. PS: Please make sure order of object should remain same

E.g. if array is of integer is given as  5 2 2 8 5 6 8 8, then we should get 8 8 8 5 5 2 2 6 , here freq. of 5 and 2 are same but 5 comes before 2 in array thus its should come before in output as well.

Here is the working code , let me know if it will fail for any test case and  if we can improve it?

/********************************************************

Time Complexity :  O(n)+O(nlogn)+O(n)=O(nlogn)

Space Complexity : Auxallery Space O(2n)= O(n)

*********************************************************/

 Run Here http://ideone.com/FQ65xM

Given a sequence of n real numbers A(1) ... A(n), determine a contiguous subsequence A(i) ... A(j) for which the sum of elements in the subsequence is maximized

#include<stdio.h>
#define MAX(a,b) ((a>b)?(a):(b))
main()
{
  int arr[]={-2, -3, 4, -1, -2, 1, 5, -3};
  int len,i;
  int max=0;
  len = sizeof(arr)/sizeof(arr[0]);
  max=arr[0];
  int finalmax=0;
  int start=0,end=0;
  for(i=1;i<len;i++)
  {
    max = MAX(max+arr[i], arr[i]); 
      
        finalmax=MAX(max,finalmax);
    
  }
 
    
      printf("MAX:%d %d %d \n",finalmax, start ,end);
 
   
   
}

Example if you want to print array http://codepad.org/BhYxSlp4

Given a root of a tree, and an integer k. Print all the nodes which are at k distance from given elment

How would you design a logging system for something like Google , you should be able to query for the number of times a URL was opened within two time frames.

i/p : start_time , end_time , URL1 

o/p : number of times URL1 was opened between start and end time.

Some specs : Database is not an optimal solution A URL might have been opened multiple times for given time stamp. A URL might have been opened a large number of times within two time stamps. start_time and end_time can be a month apart. time could be granular to a second.

Assume your daily prices of a stock are 3 7 4 10 11 8 5 4 8 . You can only buy 1 share or sell 1 share a day, but you can only sell if you own the stock. You can't hold more than 1 share. write an algo that finds the strategy that has the highest pay off. Don't generate the all possible strategies and compare.

We're playing a game. Cards numbered from 1-10 are placed in a hat. whatever card is drawn is the paid out amount. how much should i charge you to play this game? If you can redraw by placing the first card back into the hat, what is the new price?

You have N guards in a line each with a demand of coins.You can skip paying a guard only if his demand is lesser than what you have totally paid before reaching him.Find the least number of coins you spend to cross all guards

Implement LookAndSay function. For example, first, let user input a number, say 1. Then, the function will generate the next 10 numbers which satisfy this condition: 1, 11,21,1211,111221,312211... explanation: first number 1, second number is one 1, so 11. Third number is two 1(previous number), so 21. next number one 2 one 1, so 1211 and so on...

Source : Heard from Junior , EPIC visit to BIT Mesra

'K' number of char arrays of different length are given, find Cartesian product of them in optimal way & give complexity.

Source : commented by user yen