Suppose we have two strings s and t. We have to make a string called merge in the following way: while either s or t are non-empty, select one of the following options −
If s is non-empty, then append the first character in s to merge and delete it from s.
If t is non-empty, then append the first character in t to merge and delete it from t.
So we have to find the lexicographically largest merge we can make.
So, if the input is like s = "zxyxx" t = "yzxxx", then the output will be zyzxyxxxxx, because
Pick from s: merge = "z", s = "xyxx", t = "yzxxx"
Pick from t: merge = "zy", s = "xyxx", t = "zxxx"
Pick from t: merge = "zyz", s = "xyxx", t = "xxx"
Pick from s: merge = "zyzx", s = "yxx", t = "xxx"
Pick from s: merge = "zyzxy", s = "xx", t = "xxx"
Then add the remaining 5 x's from s and t at the end of merge.
To solve this, we will follow these steps −
ans := blank string
idx1 := 0, idx2 := 0
while idx1 < size of s and idx2 < size of t, do
if s[idx1] > t[idx2] or (s[idx1] is same as t[idx2] and substring of s[from index idx1 to end] >= substring of t[from index idx2 to end]), then
ans := ans concatenate s[idx1]
idx1 := idx1 + 1
otherwise when s[idx1] < t[idx2] or (s[idx1] is same as t[idx2] and substring of s[from index idx1 to end] <= substring of t[from index idx2 to end]), then
ans := ans concatenate t[idx2]
idx2 := idx2 + 1
return ans concatenate s[from index idx1 to end] concatenate t[from index idx2 to end]
Example
Let us see the following implementation to get better understanding −
def solve(s, t):
ans = ""
idx1 = idx2 = 0
while(idx1<len(s) and idx2<len(t)):
if s[idx1]>t[idx2] or (s[idx1]==t[idx2] and s[idx1:]>=t[idx2:]):
ans+=s[idx1]
idx1+=1
elif s[idx1]<t[idx2] or (s[idx1]==t[idx2] and s[idx1:]<=t[idx2:]):
ans+=t[idx2]
idx2+=1
return ans+s[idx1:]+t[idx2:]
s = "zxyxx"
t = "yzxxx"
print(solve(s, t))
Input
[7,4,5,3,8], [[0,2,2],[4,2,4],[2,13,100]]
Output
zyzxyxxxxx