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Challenges Given the preorder and the inorder of a tree, output the postorder

Ruby, 75 72 bytes f=->((e,*r),n){(i=n.index e)?f[r[0,i],n[...i]]+f[r[i..],n[i+1..]]+[e]:n} Attempt This Online!

posted 3y ago by radarek‭  ·  edited 3y ago by radarek‭

Answer
#2: Post edited by user avatar radarek‭ · 2022-01-23T16:42:44Z (almost 3 years ago)
  • # [Ruby](https://www.ruby-lang.org/), 75 bytes
  • <pre><code class="lang-ruby">f=-&gt;((e,*r),n){(i=n.index e)?[*f[r[0,i],n[...i]],*f[r[i..],n[i+1..]],e]:[]}</code></pre>
  • [Attempt This Online!](https://ato.pxeger.com/run?1=dZK_bsIwEMaljnmKEwwBekRx-BeQAlMnBiTUzXgojVNFqgwKSUWF8iRdGNqHap-mF9sB2tIhzvn7vvudE_ntPSvWr8fjR5En3fBznkTdaaslsZO1UbUPrTRSXqpiuQfZnvFOwjPuYypQcc_zUiFQS6nnVVJ6y6gQKMWEi9Igv27WudzlEEF3us3kJotlhpAqW8j9Vj7mMoZ44wBsi3wHjXvKp-pppVY51C1R81CXpTYsgXRblTRAO83Dy8NzIWliwv9MFNR9CkTn8TNwF3MXJuDeLZeLpVs2HKlix6nOzrlAMI-wgl_t7HLSEFilMAT_9P5t_ghdmghBrZ_L4EoKoYfQvwjQjrRKCHSirxP_9CEMEIYII4QQYUxWZZPPqmZKMIowyjAKMUoxijHKBfqbDNvMGWlQqIkW5FtO37IGlh1a1vAqy5xlaBBjzWMXB-lZqIUEvoFomP2N5qrVt_gb)
  • # [Ruby](https://www.ruby-lang.org/), <del>75</del> 72 bytes
  • <pre><code class="lang-ruby">f=-&gt;((e,*r),n){(i=n.index e)?f[r[0,i],n[...i]]+f[r[i..],n[i+1..]]+[e]:n}</code></pre>
  • [Attempt This Online!](https://ato.pxeger.com/run?1=dZLPasJAEMahxzzFoIdoHUM2_otC9FQo9CBIb3EPtdmUhbJKTIpF8iS9eGgfqn2azm42alt7yGb2-775zSbs23tWrF4Ph48iT7vh520adaetlsDrrI2qvW_JSHlSJWIHoj1L4yz2UXJUsed5kvOOVqTnaUV2GBW8Ews-UWXF-7pa5WKbQwTd6SYT6ywRGYJUthC7jXjMRQLJ2gHYFPkWGveUl-ppqZY51C1Rc1-XpTEsgXRblTTAOM39y8NzIWhiGv-ZyKn7GIhO42fgzu9cmIB7s1jMF27ZcIRKHEefPY45QvVwK_h6Z5ejhsC0whD84_u3-SN0biIEtX4qgwsphB5C_yxAO9K0EJhE3yT-6UMYIAwRRgghwpgsbZPPdDMlGEUYZRiFGKUYxRjlAvNNFbuaMzKg0BAtyLecvmUNLDu0rOFFVnWWYYUYGx47O0jPQi0k8CuIgdnfWF21-gp_Aw)
#1: Initial revision by user avatar radarek‭ · 2022-01-23T16:31:58Z (almost 3 years ago) 
# [Ruby](https://www.ruby-lang.org/), 75 bytes

<pre><code class="lang-ruby">f=-&gt;((e,*r),n){(i=n.index e)?[*f[r[0,i],n[...i]],*f[r[i..],n[i+1..]],e]:[]}</code></pre>

[Attempt This Online!](https://ato.pxeger.com/run?1=dZK_bsIwEMaljnmKEwwBekRx-BeQAlMnBiTUzXgojVNFqgwKSUWF8iRdGNqHap-mF9sB2tIhzvn7vvudE_ntPSvWr8fjR5En3fBznkTdaaslsZO1UbUPrTRSXqpiuQfZnvFOwjPuYypQcc_zUiFQS6nnVVJ6y6gQKMWEi9Igv27WudzlEEF3us3kJotlhpAqW8j9Vj7mMoZ44wBsi3wHjXvKp-pppVY51C1R81CXpTYsgXRblTRAO83Dy8NzIWliwv9MFNR9CkTn8TNwF3MXJuDeLZeLpVs2HKlix6nOzrlAMI-wgl_t7HLSEFilMAT_9P5t_ghdmghBrZ_L4EoKoYfQvwjQjrRKCHSirxP_9CEMEIYII4QQYUxWZZPPqmZKMIowyjAKMUoxijHKBfqbDNvMGWlQqIkW5FtO37IGlh1a1vAqy5xlaBBjzWMXB-lZqIUEvoFomP2N5qrVt_gb)