lyrically wicked - 1 year ago 71

Javascript Question

I have a string

`str`

`M`

`N`

`M`

`N`

`N`

`M`

`M`

`N`

`N`

`M=1`

`N=3`

`"aabcde"`

`var str = "aabcde";`

var result = [

["a", "a", "b", "cde"],

["a", "ab", "cde"],

["aa", "b", "cde"],

//...

["aab", "cde"],

["aab", "cd", "e"],

["aab", "c", "de"],

["aab", "c", "d", "e"]

]

What is the efficient way to solve this, avoiding unnecessary intermediate subarrays? I don't want to generate all possible combinations, and then delete each subarray if it contains at least one substring with inacceptable length. Is there another way, without unnecessary computations?

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Answer Source

This effectively boils down to generating restricted integer compositions with parts between two values `M`

and `N`

. It is a simple matter to generate such compositions recursively.

I also noticed in your example for `"aabcde", M=1, N=3"`

that your array lengths were all less than or equal to `4`

in length, so I also included an optional parameter to restrict the number of parts in each composition.

```
function* restrictedCompositions(n, a, b, k = n) {
if (!(0 < a && a <= b && b <= n && 0 < k && k <= n)) {
throw "invalid arguments";
}
let C = [];
function* recGen(m, r) {
if (m == 0) {
yield C; // client must copy if they wish to store value for later
}
else {
let y = Math.min(b, m);
let x = Math.max(a, m - y*(r - 1));
for (let v = x; v <= y; v++) {
C.push(v);
yield* recGen(m - v, r - 1);
C.pop();
}
}
}
yield* recGen(n, k);
}
function* generateChoppedStrings(str, M, N, K = str.length) {
for (let composition of restrictedCompositions(str.length, M, N, K)) {
let chopped = [];
let i = 0;
for (let part of composition) {
let j = i + part;
chopped.push(str.slice(i, j));
i = j;
}
yield chopped;
}
}
function chopString(str, M, N, K = str.length) {
for (let chopped of generateChoppedStrings(str, M, N, K)) {
console.log(chopped);
}
}
chopString("aabcde", 1, 3, 4);
```

Output:

```
["a", "a", "b", "cde"]
["a", "a", "bc", "de"]
["a", "a", "bcd", "e"]
["a", "ab", "c", "de"]
["a", "ab", "cd", "e"]
["a", "ab", "cde"]
["a", "abc", "d", "e"]
["a", "abc", "de"]
["aa", "b", "c", "de"]
["aa", "b", "cd", "e"]
["aa", "b", "cde"]
["aa", "bc", "d", "e"]
["aa", "bc", "de"]
["aa", "bcd", "e"]
["aab", "c", "d", "e"]
["aab", "c", "de"]
["aab", "cd", "e"]
["aab", "cde"]
```

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