Maximum segment value after putting k breakpoints in a number

3

Given a large number as string s and an integer k which denotes the number of breakpoints we must put in the number k <= string length. The task is to find maximum segment value after putting exactly k breakpoints.

Examples:

Input : s = "8754", k = 2
Output : Maximum number = 87
Explanation : We need to two breakpoints. After
putting the breakpoints, we get following options
8 75 4
87 5 4
The maximum segment value is 87.

Input : s = "999", k = 1 
Output : Maximum Segment Value = 99
Explanation : We need to one breakpoint. After
putting the breakpoint, we either get 99,9 or
9,99.

One important observation is, the maximum would always be of length “string-length – k” which is the maximum value of any segment. Considering the fact, problem becomes like sliding window problem means we need to find maximum of all substrings of size (string-length – k).

// CPP program to find the maximum segment
// value after putting k breaks.
#include <bits/stdc++.h>
using namespace std;

// Function to Find Maximum Number
int findMaxSegment(string &s, int k) {

  // Maximum segment length
  int seg_len = s.length() - k;

  // Find value of first segment of seg_len
  int res = 0;
  for (int i=0; i<seg_len; i++)
     res = res * 10 + (s[i] - '0');

  // Find value of remaining segments using sliding
  // window
  int seg_len_pow = pow(10, seg_len-1);
  int curr_val = res;
  for (int i = 1; i <= (s.length() - seg_len); i++) {

    // To find value of current segment, first remove
    // leading digit from previous value    
    curr_val = curr_val - (s[i-1]- '0')*seg_len_pow;

    // Then add trailing digit
    curr_val = curr_val*10 + (s[i+seg_len-1]- '0');

    res = max(res, curr_val);
  }
  return res;
}

// Driver's Function
int main() {
  string s = "8754";
  int k = 2;
  cout << "Maximum number = " << findMaxSegment(s, k);
  return 0;
}
Output:

Maximum number = 87

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