Test results - Codility

Tasks Details

easy

1. Brackets

Determine whether a given string of parentheses (multiple types) is properly nested.

100%

A string S consisting of N characters is considered to be properly nested if any of the following conditions is true:

S is empty;

S has the form "(U)" or "[U]" or "{U}" where U is a properly nested string;

S has the form "VW" where V and W are properly nested strings.

For example, the string "{[()()]}" is properly nested but "([)()]" is not.

Write a function:

class Solution { public int solution(String S); }

that, given a string S consisting of N characters, returns 1 if S is properly nested and 0 otherwise.

For example, given S = "{[()()]}", the function should return 1 and given S = "([)()]", the function should return 0, as explained above.

Write an efficient algorithm for the following assumptions:

N is an integer within the range [0..200,000];

string S is made only of the following characters: '(', '{', '[', ']', '}' and/or ')'.

Solution

Programming language used Java 8

Time spent on task 24 minutes

Notes

not defined yet

Code: 11:08:01 UTC, java, verify, result: Passed

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// you can also use imports, for example:
// import java.util.*;
import java.util.Stack;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");

class Solution {
    public int solution(String S) {
        Stack<Character> stack = new Stack<>();
        if (S.length() == 0) {
            return 1;
        }
        for (int i=0; i<S.length(); i++) {
            if (S.charAt(i) == '(' || S.charAt(i) == '{' || S.charAt(i) == '[') {
                stack.push(S.charAt(i));
            } else {
                if (stack.isEmpty()) {
                    return 0;
                }

                char preChar = stack.pop();
                if (S.charAt(i) == ')' && preChar != '(') {
                    return 0;
                }
                if (S.charAt(i) == '}' && preChar != '{') {
                    return 0;
                }
                if (S.charAt(i) == ']' && preChar != '[') {
                    return 0;
                }
            }
        }
        if (!stack.isEmpty()) {
            return 0;
        }
        return 1;
    }
}

Analysis

▶

example1
example test 1

✔

▶

example2
example test 2

✔

Code: 11:08:06 UTC, java, final, score: 100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

// you can also use imports, for example:
// import java.util.*;
import java.util.Stack;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");

class Solution {
    public int solution(String S) {
        Stack<Character> stack = new Stack<>();
        if (S.length() == 0) {
            return 1;
        }
        for (int i=0; i<S.length(); i++) {
            if (S.charAt(i) == '(' || S.charAt(i) == '{' || S.charAt(i) == '[') {
                stack.push(S.charAt(i));
            } else {
                if (stack.isEmpty()) {
                    return 0;
                }

                char preChar = stack.pop();
                if (S.charAt(i) == ')' && preChar != '(') {
                    return 0;
                }
                if (S.charAt(i) == '}' && preChar != '{') {
                    return 0;
                }
                if (S.charAt(i) == ']' && preChar != '[') {
                    return 0;
                }
            }
        }
        if (!stack.isEmpty()) {
            return 0;
        }
        return 1;
    }
}

Analysis summary

The solution obtained perfect score.

Analysis

Detected time complexity:

O(N)

▶

example1
example test 1

✔

▶

example2
example test 2

✔

▶

negative_match
invalid structures

✔

▶

empty
empty string

✔

▶

simple_grouped
simple grouped positive and negative test, length=22

✔

▶

large1
simple large positive test, 100K ('s followed by 100K )'s + )(

✔

▶

large2
simple large negative test, 10K+1 ('s followed by 10K )'s + )( + ()

✔

▶

large_full_ternary_tree
tree of the form T=(TTT) and depth 11, length=177K+

✔

▶

multiple_full_binary_trees
sequence of full trees of the form T=(TT), depths [1..10..1], with/without some brackets at the end, length=49K+

✔

▶

broad_tree_with_deep_paths
string of the form [TTT...T] of 300 T's, each T being '{{{...}}}' nested 200-fold, length=120K+

✔