# \#500 Keyboard Row
## *給定字串陣列words, 回傳該陣列中, 該字串都位於鍵盤上的同一行的字串(陣列型態)*
## Log
- build 20210926 by syhuang

## Set差集解
- 把鍵盤三行字串和input轉為Set做差集比較
- 只要其中一行的差集為空集合, 就表示該字串的字都在那一行
- javascript"空集合"用Array.length=0來做判斷
- leetcode submit runtime 91%, memory 5%

Set.prototype.difference = function(setB) {
    var difference = new Set(this);
    for (var elem of setB) {
        difference.delete(elem);
    }
    return difference;
}
var findWords = function(words) {
    const rowASet = new Set('qwertyuiop');
    const rowBSet = new Set('asdfghjkl');
    const rowCSet = new Set('zxcvbnm');
    let result = [];
    for(const word of words){
        const wordSet = new Set(word.toLowerCase());
        let inOneRowSet = false;
        //與三個row做差集, 只要其中一個row差集為空集合, 就表示該word屬於該row
        if(Array.from(wordSet.difference(rowASet)).length === 0 ||
           Array.from(wordSet.difference(rowBSet)).length === 0 ||
           Array.from(wordSet.difference(rowCSet)).length === 0)
            inOneRowSet = true;
        if(inOneRowSet) result.push(word);
    }
    return result;
};

## 初見
- 對words的每個字串的每個字元跑迴圈, 都在同一行就滿足題意
- leetcode submit runtime 13%, memory 88%

var findWords = function(words) {
    const rows = ['qwertyuiop','asdfghjkl','zxcvbnm'];
    let result = [];
    for(let word of words){
        const lowerCaseWord = word.toLowerCase();
        //判斷word內每個字元是否在同一行
        let preRowIndex = -1;
        let withSameRowIndex = true;
        outLoop:
        for(const char of lowerCaseWord){
            for(const rowIndex in rows){
                if(rows[rowIndex].indexOf(char)>-1){
                    if(preRowIndex!=-1 && rowIndex!=preRowIndex){
                        withSameRowIndex = false;
                        break outLoop;
                    }
                    else preRowIndex = rowIndex;
                }
            }            
        }
        if(withSameRowIndex) result.push(word);
    }
    return result;
};

## 備註
## 參考
- [參考解](https://leetcode.com/problems/keyboard-row/discuss/97913/Easy-Understand-Solution)
###### tags: `leetcode`, `leetcode-easy`, `set`, `array`, `applaction`