Hand of Straights

MEDIUM✓ CHIP-TIMEDLC #846 — FULL STATEMENT ↗

The drill: A hand of cards must be dealt entirely into equal-size groups, each group a run of consecutive values with no gaps and no repeats inside it. Decide whether such a full dealing is possible.

THE BRIEFING — THE FULL DRILL, IN MY OWN WORDS

A hand of number cards needs to be split entirely into groups of a fixed size, with nothing left over. Each group must form an unbroken run of consecutive values — no gaps, and no value repeated within the same group.

Every single card in the hand has to end up in exactly one group; cards can't be discarded or held back, and a card's value can repeat across the whole hand as long as no two copies land in the same group.

The verdict needed is simply whether such a complete grouping exists for the given hand and group size — not what the groups actually look like.

EX 01

hand = [3, 4, 2, 5, 6, 1] · groupSize = 3

→ true

TWO CLEAN CONSECUTIVE TRIPLES

EX 02

hand = [1, 2, 3, 4, 5] · groupSize = 4

→ false

HAND SIZE NOT DIVISIBLE BY GROUPSIZE

EX 03

hand = [1, 2, 3, 3, 4, 5] · groupSize = 3

→ true

A DUPLICATE FEEDS TWO OVERLAPPING GROUPS

the hand size must divide evenly by the group size, or grouping fails
card values can repeat across the hand, within reasonable numeric ranges
every group is a run of consecutive values with no duplicate inside it
every card in the hand must be used — none may be left ungrouped

THE HINTS — TAKE ONLY WHAT YOU NEED

HINT 1 THE NUDGE

The smallest remaining card has nowhere else to go — it can only ever be the START of a group, since no smaller card exists to extend below it. That fixes every group's first move.

HINT 2 THE STRUCTURE

So the strategy isn't really a choice: always start the next group at whatever card is currently smallest, and require the next groupSize−1 consecutive values to exist. Track how many of each value remain.

HINT 3 ONE STEP FROM THE ANSWER

Count every value; walk values from smallest to largest, and whenever a value still has cards left, consume groupSize copies of it and each of the next groupSize−1 values immediately. Any missing value fails the whole hand.

COACH'S BOARD — THE PATTERN, STEP BY STEP

SMALLEST FIRSTPATTERN · GREEDY — COUNT MAPhand = [3, 4, 2, 5, 6, 1] · groupSize = 3

COUNTS REMAINING

1 → 1

2 → 1

3 → 1

4 → 1

5 → 1

6 → 1

STEP 1

Hand [3,4,2,5,6,1], groupSize 3. Sorted, every value's count starts at 1 — walk smallest to largest.

STEP 1 / 6 · ← → WORK TOO

THE SPLITS — TWO PACES, TWO LANGUAGES

grind/hand-of-straights.py — RACE PACE

LANG ▸

PACE ▸

class Solution:
    def isNStraightHand(self, hand: List[int], groupSize: int) -> bool:
        if len(hand) % groupSize != 0:
            return False
        count = collections.Counter(hand)
        for card in sorted(count):
            need = count[card]
            if need <= 0:
                continue
            for k in range(card, card + groupSize):
                if count[k] < need:
                    return False
                count[k] -= need
        return True

TIME O(N LOG N)SPACE O(N)PYTHON · RACE PACE · 14 LN

class Solution:
    def isNStraightHand(self, hand: List[int], groupSize: int) -> bool:
        if len(hand) % groupSize != 0:
            return False
        remaining = sorted(hand)
        while remaining:
            start = remaining[0]
            temp = list(remaining)
            for card in range(start, start + groupSize):
                if card not in temp:
                    return False
                temp.remove(card)  # linear scan + shift, the naive part
            remaining = temp
        return True

TIME O(N²)SPACE O(N)PYTHON · TRAINING PACE · 14 LN

class Solution {
    public boolean isNStraightHand(int[] hand, int groupSize) {
        if (hand.length % groupSize != 0) {
            return false;
        }
        TreeMap<Integer, Integer> count = new TreeMap<>();
        for (int card : hand) {
            count.merge(card, 1, Integer::sum);
        }
        for (int card : new ArrayList<>(count.keySet())) {
            int need = count.getOrDefault(card, 0);
            if (need <= 0) {
                continue;
            }
            for (int k = card; k < card + groupSize; k++) {
                int have = count.getOrDefault(k, 0);
                if (have < need) {
                    return false;
                }
                count.put(k, have - need);
            }
        }
        return true;
    }
}

TIME O(N LOG N)SPACE O(N)JAVA · RACE PACE · 25 LN

class Solution {
    public boolean isNStraightHand(int[] hand, int groupSize) {
        if (hand.length % groupSize != 0) {
            return false;
        }
        List<Integer> remaining = new ArrayList<>();
        for (int card : hand) {
            remaining.add(card);
        }
        Collections.sort(remaining);
        while (!remaining.isEmpty()) {
            int start = remaining.get(0);
            for (int card = start; card < start + groupSize; card++) {
                int idx = remaining.indexOf(card); // linear scan, the naive part
                if (idx == -1) {
                    return false;
                }
                remaining.remove(idx);
            }
        }
        return true;
    }
}

TIME O(N²)SPACE O(N)JAVA · TRAINING PACE · 23 LN

✓ CHIP-TIMED — ALL 4 SOLUTIONS RAN GREEN AGAINST SELF-AUTHORED CASES IN CI · JDK 21 · CPYTHON 3.12 · NOTHING PUBLISHES RED