Healthkart.com Campus Selection Procedure

Would you be able to share the programming questions asked in the coding round? That'd be interesting!

There were 2 Questions initially, with no time limit.
1. Given a text file or a large string. Find the minimum number of characters b/w any two words.
E.g.- The string is "he used to be a boy but now he is a man"
The minimum no. of characters b/w "he" and "boy" (can also be b/w "boy" and "he") is 9 (including spaces).
Optimize this code with minimum computations, iterations and extra spaces.
Improve the code such that it only finds the minimum number of characters only b/w "he" and "boy" (not b/w "boy" and "he") as per given example. In this case, the answer would be 14 (including spaces).
2. There are two string. Remove the characters from the first string, which have been occurred in the second string.
E.g. - First String - "I am a boy"
Second String - "mb" (This string should have distinct characters)
Result - "I a a by"
Improve the code with minimum computations and the result should be stored in the given first string itself.
Additional Coding Questions after completing the above two.
3. Find the sub-array in an array of integers having maximum sum.
4. There is a n-square matrix, where every cell is assigned a weight in +ve interger. Starting from bottom left corner, find the path with maximum weight to reach its diagonally opposite. You're allowed to move either right or up direction.
Optimize these codes with minimum computations, iterations and extra space.