Left path cloud recursion + dynamic planning

recursive

Print all subsequences in the string

str = “abc”
Print

Print all subsequences in the string , No subsequence of repeated literals

Print all permutations of a string

Full Permutation ： A string “abc" All characters in must be in different order
abc The whole arrangement

Example diagram of violent solution

Technical solution

Print all permutations of a string , Don't repeat the arrangement

You can also use the final result set Set save , But it has high efficiency without using shear directly ,set Is to filter in the final result set , Pruning is to directly filter out branches that do not need to be run

Data in the reverse stack cannot use additional memory