BFS
var ladderLength = function(beginWord, endWord, wordList) { let dict=new Set(wordList); if(!dict.has(endWord)) return 0; queue=[]; queue.push(beginWord); let len=beginWord.length; var depth=0; while(queue.length>0){ depth++; var size=queue.length; while(size-->0){ var head=queue.shift(); for(var i=0;i<len;i++){ for(var j=97;j<=122;j++){ var temp=head.substring(0,i)+String.fromCharCode(j)+head.substr(i+1); if(temp==endWord) return depth+1; if(!dict.has(temp)) continue; dict.delete(temp); queue.push(temp); } } } } return 0; };
