해시 테이블

Hash table

키를 해시값으로 바꿔 버킷 위치를 찾는 키·값 저장소.

···
css
body{display:block} .stage{position:absolute;inset:0;display:flex;flex-direction:column;padding:clamp(9px,3vmin,20px);gap:5px}
.top{display:flex;align-items:center;justify-content:space-between;gap:8px;font-size:clamp(11px,2.7vmin,14px);font-weight:700;white-space:nowrap}
.top span:last-child{color:var(--muted);font-weight:500}canvas{width:100%;height:0;flex:1 1 0;min-height:0}
.controls{display:none;align-items:center;gap:9px;font-size:12px;color:var(--muted)}
button{border:1px solid var(--line);background:var(--surface);color:var(--fg);border-radius:7px;padding:5px 10px;cursor:pointer}
input{width:100px;accent-color:var(--accent)}
@media(min-width:600px){.controls{display:flex}}
js
const ALGORITHM_KIND = "hash-table";

const kind = ALGORITHM_KIND;
const root = document.createElement('div'); root.className = 'stage';
root.innerHTML = '<div class="top"><span id="state"></span><span id="count"></span></div><canvas></canvas><div class="controls"><button id="reset">다시 시작</button><button id="step">한 단계</button><label>속도 <input id="speed" type="range" min="1" max="5" value="3"></label></div>';
document.body.append(root);
const canvas = root.querySelector('canvas'), ctx = canvas.getContext('2d');
const title = root.querySelector('#state'), count = root.querySelector('#count');
const style = getComputedStyle(document.documentElement);
const colors = Object.fromEntries(['bg','fg','muted','line','accent','accent-2','accent-3','surface'].map(k => [k, style.getPropertyValue('--' + k).trim()]));
const palette = {base:colors.accent, active:colors['accent-2'], done:colors['accent-3'], text:colors.fg, faint:colors.muted, line:colors.line, surface:colors.surface};
let generation = 0, states = [], index = 0, elapsed = 0;
function rng(seed){return function(){seed |= 0;seed = seed + 0x6D2B79F5 | 0;let t = Math.imul(seed ^ seed >>> 15, 1 | seed);t = t + Math.imul(t ^ t >>> 7, 61 | t) ^ t;return ((t ^ t >>> 14) >>> 0) / 4294967296}}
function shuffled(){const a=[3,8,2,7,4,9,1,6,5];const random=rng(42+generation*23);for(let i=a.length-1;i>0;i--){const j=Math.floor(random()*(i+1));[a[i],a[j]]=[a[j],a[i]]}return a}
function push(values, active=[], done=[], note='', extra={}){states.push({values:[...values],active:[...active],done:[...done],note,extra})}
function makeStates(){
  states=[];
  const a=shuffled(), n=a.length;
  push(a,[],[],'시작');
  if(kind==='big-o') {states=[];for(let size=1;size<=12;size++)push([],[],[],'입력 크기 n = '+size,{size});return}
  if(kind==='bubble-sort'){for(let end=n-1;end>0;end--){for(let j=0;j<end;j++){push(a,[j,j+1],Array.from({length:n-end-1},(_,k)=>n-1-k),'이웃한 두 값 비교');if(a[j]>a[j+1]){[a[j],a[j+1]]=[a[j+1],a[j]];push(a,[j,j+1],[],'순서가 반대라 교환')}}push(a,[],Array.from({length:n-end},(_,k)=>n-1-k),'가장 큰 값 확정')}push(a,[],a.map((_,i)=>i),'정렬 완료')}
  if(kind==='selection-sort'){for(let i=0;i<n;i++){let min=i;for(let j=i+1;j<n;j++){push(a,[min,j],Array.from({length:i},(_,k)=>k),'최솟값 탐색');if(a[j]<a[min])min=j}[a[i],a[min]]=[a[min],a[i]];push(a,[i,min],Array.from({length:i+1},(_,k)=>k),'최솟값을 앞에 배치')}}
  if(kind==='insertion-sort'){for(let i=1;i<n;i++){let j=i;while(j>0&&a[j-1]>a[j]){push(a,[j-1,j],[],'앞의 값과 비교');[a[j-1],a[j]]=[a[j],a[j-1]];push(a,[j-1,j],Array.from({length:i+1},(_,k)=>k),'왼쪽으로 삽입');j--}push(a,[],Array.from({length:i+1},(_,k)=>k),'왼쪽 부분 정렬됨')}}
  if(kind==='merge-sort'){function merge(lo,hi){if(hi-lo<=1)return;const mid=(lo+hi)>>1;push(a,Array.from({length:hi-lo},(_,i)=>lo+i),[],'구간 분할: '+lo+'–'+(hi-1));merge(lo,mid);merge(mid,hi);const sorted=[...a.slice(lo,mid)], right=[...a.slice(mid,hi)];let l=0,r=0;for(let k=lo;k<hi;k++){a[k]=r>=right.length||(l<sorted.length&&sorted[l]<=right[r])?sorted[l++]:right[r++];push(a,[k],Array.from({length:k-lo+1},(_,i)=>lo+i),'작은 값부터 병합')}}merge(0,n);push(a,[],a.map((_,i)=>i),'정렬 완료')}
  if(kind==='quick-sort'){function quick(lo,hi){if(lo>=hi)return;const pivot=a[hi];let i=lo;push(a,[hi],[],'피벗 '+pivot+' 선택');for(let j=lo;j<hi;j++){push(a,[j,hi],[],'피벗과 비교');if(a[j]<pivot){[a[i],a[j]]=[a[j],a[i]];push(a,[i,j],[],'작은 값을 왼쪽으로');i++}}[a[i],a[hi]]=[a[hi],a[i]];push(a,[i],[i],'피벗 자리 확정');quick(lo,i-1);quick(i+1,hi)}quick(0,n-1);push(a,[],a.map((_,i)=>i),'정렬 완료')}
  if(kind==='heap-sort'){function sift(size,i){while(2*i+1<size){let child=2*i+1;if(child+1<size&&a[child+1]>a[child])child++;push(a,[i,child],[],'부모와 큰 자식 비교');if(a[i]>=a[child])break;[a[i],a[child]]=[a[child],a[i]];push(a,[i,child],[],'큰 값을 위로');i=child}}for(let i=(n>>1)-1;i>=0;i--)sift(n,i);for(let end=n-1;end>0;end--){[a[0],a[end]]=[a[end],a[0]];push(a,[0,end],Array.from({length:n-end},(_,k)=>end+k),'최댓값을 끝으로');sift(end,0)}push(a,[],a.map((_,i)=>i),'정렬 완료')}
  if(kind==='counting-sort'){const freq=Array(10).fill(0);for(let i=0;i<n;i++){freq[a[i]]++;push(freq,[a[i]],[],'값 '+a[i]+'의 개수 세기',{histogram:true})}let k=0;for(let value=1;value<=9;value++)while(freq[value]-- > 0){a[k++]=value;push(a,[k-1],Array.from({length:k},(_,i)=>i),'개수대로 출력')}push(a,[],a.map((_,i)=>i),'정렬 완료')}
  if(kind==='binary-search'){states=[];const b=[1,2,3,4,5,6,7,8,9];let lo=0,hi=8,target=7;push(b,[],[],'정렬된 배열에서 7 찾기');while(lo<=hi){let mid=(lo+hi)>>1;push(b,[mid],[],'가운데 '+b[mid]+'와 비교',{range:[lo,hi]});if(b[mid]===target){push(b,[mid],[mid],'7 찾음');break}if(b[mid]<target)lo=mid+1;else hi=mid-1;push(b,[],[],'절반 제외',{range:[lo,hi]})}}
  if(kind==='two-pointers'){states=[];const b=[1,2,3,4,5,6,7,8,9];let l=0,r=8;push(b,[l,r],[],'합계 10 찾기');while(l<r){push(b,[l,r],[],'합 '+(b[l]+b[r])+' 비교');if(b[l]+b[r]===10){push(b,[l,r],[l,r],'합계 10인 쌍');l++;r--}else if(b[l]+b[r]<10)l++;else r--}}
  if(kind==='sliding-window'){states=[];const b=[2,1,4,3,5,2,6,1,4];let sum=b.slice(0,3).reduce((x,y)=>x+y,0);push(b,[0,1,2],[],'크기 3, 합 '+sum);for(let start=1;start<=b.length-3;start++){sum+=b[start+2]-b[start-1];push(b,[start,start+1,start+2],[],'왼쪽 제거 · 오른쪽 추가 → 합 '+sum)}}
  if(kind==='stack'||kind==='queue'){states=[];const b=[];const acts=kind==='stack'?[['push',3],['push',8],['push',2],['pop'],['push',7],['pop'],['pop']]:[['enqueue',3],['enqueue',8],['enqueue',2],['dequeue'],['enqueue',7],['dequeue'],['dequeue']];push(b,[],[],'빈 '+(kind==='stack'?'스택':'큐'));for(const [op,value] of acts){let changed;if(op==='push'||op==='enqueue'){b.push(value);changed=b.length-1}else{changed=kind==='stack'?b.length-1:0;b.splice(changed,1)}push(b,[Math.max(0,Math.min(changed,b.length-1))],[],op+(value?' '+value:''),{operation:op})}}
  if(kind==='linked-list'){states=[];const nodes=[3,8,2,7].map(value=>({value,next:null}));for(let i=0;i<nodes.length-1;i++)nodes[i].next=nodes[i+1];const head=nodes[0];function snapshot(){const result=[];for(let node=head;node;node=node.next)result.push(node.value);return result}push(snapshot(),[],[],'노드와 다음 포인터');let node=head,i=0;while(node){push(snapshot(),[i++],[],'처음부터 '+node.value+' 방문');node=node.next}nodes[1].next={value:5,next:nodes[1].next};push(snapshot(),[2],[],'포인터 연결을 바꿔 5 삽입');node=head;i=0;while(node){push(snapshot(),[i++],[],'다시 순회: '+node.value);node=node.next}}
  if(kind==='hash-table'){states=[];const names=['A','F','B','G','C','H'];const buckets=Array.from({length:5},()=>[]);push([],[],[],'5개 버킷',{buckets:buckets.map(x=>[...x])});for(const name of names){const bucket=(name.charCodeAt(0)-65)%5;buckets[bucket].push(name);push([], [bucket],[],'키 '+name+' → 버킷 '+bucket,{buckets:buckets.map(x=>[...x])})}}
  if(kind==='binary-search-tree'){states=[];const order=[5,3,8,1,4,7,9],tree=[];for(const value of order){let i=0;while(tree[i]!==undefined)i=value<tree[i]?2*i+1:2*i+2;tree[i]=value;push(tree,[i],[],'값 '+value+' 삽입',{tree:true})}let i=0;while(tree[i]!==4){push(tree,[i],[],'4와 '+tree[i]+' 비교',{tree:true});i=4<tree[i]?2*i+1:2*i+2}push(tree,[i],[i],'값 4 찾음',{tree:true})}
  if(kind==='heap-priority-queue'){states=[];const h=[];function insert(x){h.push(x);let i=h.length-1;push(h,[i],[],'우선순위 '+x+' 추가');while(i>0){let p=(i-1)>>1;if(h[p]>=h[i])break;[h[i],h[p]]=[h[p],h[i]];i=p;push(h,[i],[],'큰 값을 부모로')}}for(const x of [3,8,2,7,5])insert(x);for(let t=0;t<2;t++){const max=h[0];h[0]=h.pop();push(h,[0],[],'최댓값 '+max+' 꺼냄');let i=0;while(2*i+1<h.length){let c=2*i+1;if(c+1<h.length&&h[c+1]>h[c])c++;if(h[i]>=h[c])break;[h[i],h[c]]=[h[c],h[i]];i=c;push(h,[i],[],'힙 복구')}}}
  if(kind==='recursion'){states=[];for(let d=1;d<=5;d++)push(Array.from({length:d},(_,i)=>5-i),[d-1],[],'factorial('+ (6-d) +') 호출',{call:true});let result=1;for(let d=5;d>=1;d--){result*=6-d;push(Array.from({length:d-1},(_,i)=>5-i),[],[],'반환값 '+result,{call:true})}}
  if(kind==='divide-and-conquer'){states=[];const b=[8,3,7,2,6,1,5,4];function visit(lo,hi){push(b,Array.from({length:hi-lo},(_,i)=>lo+i),[],'범위 '+lo+'–'+(hi-1)+' 분할',{range:[lo,hi-1]});if(hi-lo>1){const mid=(lo+hi)>>1;visit(lo,mid);visit(mid,hi);const left=b.slice(lo,mid),right=b.slice(mid,hi);let l=0,r=0;for(let k=lo;k<hi;k++)b[k]=r>=right.length||(l<left.length&&left[l]<=right[r])?left[l++]:right[r++];push(b,Array.from({length:hi-lo},(_,i)=>lo+i),[],'작은 결과를 병합')}}visit(0,b.length);push(b,[],b.map((_,i)=>i),'전체 결과')}
  if(kind==='prefix-sum'){states=[];const b=[2,1,4,3,5,2,6,1,4], prefix=[0];push(b,[],[],'원본 배열',{prefix:[0]});for(let i=0;i<b.length;i++){prefix.push(prefix[i]+b[i]);push(b,[i],Array.from({length:i+1},(_,j)=>j),'누적합 P['+(i+1)+'] = '+prefix[i+1],{prefix:[...prefix]})}push(b,[2,3,4,5],[],'구간 2–5 합 = P[6] − P[2] = '+(prefix[6]-prefix[2]),{prefix:[...prefix]})}
}
function resize(){const dpr=Math.min(devicePixelRatio||1,2);const w=canvas.clientWidth,h=canvas.clientHeight;canvas.width=Math.max(1,Math.round(w*dpr));canvas.height=Math.max(1,Math.round(h*dpr));ctx.setTransform(dpr,0,0,dpr,0,0);draw()}
function text(value,x,y,size=12,color=palette.text,align='center'){ctx.fillStyle=color;ctx.font='600 '+size+'px system-ui,sans-serif';ctx.textAlign=align;ctx.fillText(String(value),x,y)}
function round(x,y,w,h,r=7){ctx.beginPath();ctx.roundRect(x,y,w,h,r)}
function draw(){if(!states.length)return;const s=states[index], w=canvas.clientWidth,h=canvas.clientHeight;ctx.clearRect(0,0,canvas.width,canvas.height);title.textContent=s.note;count.textContent=(index+1)+' / '+states.length;const values=s.values;
 if(kind==='big-o'){const pad=26,gw=w-pad*2,gh=h-48;ctx.strokeStyle=palette.line;ctx.beginPath();ctx.moveTo(pad,12);ctx.lineTo(pad,h-27);ctx.lineTo(w-pad,h-27);ctx.stroke();const curves=[['O(1)',x=>1,palette.done],['O(log n)',x=>Math.log2(x+1)*5,palette.base],['O(n)',x=>x*3,palette.active],['O(n²)',x=>x*x*.65,palette.faint]];for(const [label,fn,color] of curves){ctx.strokeStyle=color;ctx.lineWidth=2;ctx.beginPath();for(let x=1;x<=s.extra.size;x++){const px=pad+(x/12)*gw,py=h-27-Math.min(gh,fn(x)/100*gh);if(x===1)ctx.moveTo(px,py);else ctx.lineTo(px,py)}ctx.stroke()}curves.forEach(([label,_,color],i)=>text(label,pad+38+i*(gw/4),h-6,10,color));return}
 if(kind==='hash-table'){const buckets=s.extra.buckets;const gap=w/5;for(let i=0;i<5;i++){const x=i*gap+gap*.08;round(x,h*.18,gap*.84,h*.64);ctx.fillStyle=s.active.includes(i)?palette.active:palette.surface;ctx.fill();ctx.strokeStyle=palette.line;ctx.stroke();text(i,x+gap*.42,h*.14,12,palette.faint);buckets[i].forEach((v,j)=>text(v,x+gap*.42,h*.3+j*20,12,s.active.includes(i)?colors.bg:palette.text))}return}
 if(kind==='binary-search-tree'||kind==='heap-priority-queue'){const nodes=values;const positions=[];for(let i=0;i<nodes.length;i++){const depth=Math.floor(Math.log2(i+1)),first=2**depth-1,slot=i-first;positions.push([(slot+1)*w/(2**depth+1),(depth+1)*h/4])}ctx.strokeStyle=palette.line;for(let i=1;i<nodes.length;i++){const p=(i-1)>>1;ctx.beginPath();ctx.moveTo(...positions[p]);ctx.lineTo(...positions[i]);ctx.stroke()}nodes.forEach((v,i)=>{const [x,y]=positions[i];ctx.beginPath();ctx.arc(x,y,Math.min(17,w/22),0,Math.PI*2);ctx.fillStyle=s.active.includes(i)?palette.active:palette.base;ctx.fill();text(v,x,y+4,12,colors.bg)});return}
 if(kind==='stack'||kind==='queue'||kind==='linked-list'||kind==='recursion'){const gap=w/Math.max(6,values.length+1);values.forEach((v,i)=>{const x=(i+1)*gap-gap*.34,y=h*.3;round(x,y,gap*.68,h*.33);ctx.fillStyle=s.active.includes(i)?palette.active:palette.base;ctx.fill();text(v,x+gap*.34,y+h*.19,14,colors.bg);if(kind==='linked-list'&&i<values.length-1)text('→',x+gap*.84,y+h*.2,16,palette.faint)});if(kind==='stack')text('위쪽에서 넣고 꺼냄',w/2,h*.83,11,palette.faint);if(kind==='queue')text('앞에서 꺼내고 뒤에 넣음',w/2,h*.83,11,palette.faint);if(kind==='recursion')text('호출 스택의 깊이',w/2,h*.83,11,palette.faint);return}
 const n=values.length,gap=w/(n+1),barWidth=Math.min(gap*.74,44),max=Math.max(9,...values);for(let i=0;i<n;i++){const x=(i+1)*gap-barWidth/2,barH=Math.max(7,values[i]/max*(h-42));const active=s.active.includes(i),done=s.done.includes(i);const outOfRange=s.extra.range&&(i<s.extra.range[0]||i>s.extra.range[1]);round(x,h-23-barH,barWidth,barH,Math.min(6,barWidth/4));ctx.fillStyle=outOfRange?palette.line:active?palette.active:done?palette.done:palette.base;ctx.fill();text(values[i],x+barWidth/2,h-7,Math.min(12,Math.max(9,gap*.3)),palette.text)}
 if(s.extra.prefix){const p=s.extra.prefix;text('P: '+p.join('  '),w/2,14,Math.min(12,w/30),palette.faint)}
}
function advance(){index=(index+1)%states.length;draw()}
function startIndex(){return kind==='big-o'?5:kind==='heap-priority-queue'?2:0}
function reset(){generation++;makeStates();index=startIndex();draw()}
root.querySelector('#reset').addEventListener('click',reset);root.querySelector('#step').addEventListener('click',advance);
addEventListener('resize',resize);makeStates();index=startIndex();resize();const speed=root.querySelector('#speed');setInterval(()=>{if(document.hidden)return;elapsed+=100;const baseDelay=kind==='divide-and-conquer'?1500:1050;if(elapsed>=baseDelay-Number(speed.value)*160){elapsed=0;advance()}},100);

사람 이름을 규칙에 따라 서랍 번호로 바꿔 넣으면, 다시 이름으로 같은 서랍을 바로 찾을 수 있습니다.

해시 함수로 키의 버킷 인덱스를 계산해 저장·조회합니다. 다른 키가 같은 버킷에 오면 충돌이므로 체이닝이나 열린 주소법으로 해결합니다. 좋은 분포와 적절한 부하율에서는 평균 O(1), 충돌이 심하면 최악 O(n)입니다.

정확한 키로 값을 찾는 사전·캐시에 적합합니다. 순서대로 훑거나 범위 검색할 때는 다른 구조가 낫고, 해시값 자체를 유일한 키라고 착각하면 충돌로 데이터가 사라집니다.

언제 쓰나

키로 값을 빠르게 저장하고 찾아야 할 때.

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