think of the input as 2D array

`_ _ _ _

| a b b c

| a b e

| a b

scan each column left to right. append i'th column char before incrementing. return answer if there's an empty string or if there's undefined or if there's a different character.

```
var longestCommonPrefix = (strs) => {
if(strs[0]===''||strs.length===0) return '';
let ans = '';
for(let i=0; i<strs[0].length; i++){
let curChar = strs[0][i];
for(let j=0; j<strs.length; j++)
if(strs[j][i]!==curChar || !strs[j][i] || strs[j]==='') return ans;
ans+=curChar;
}
return ans;
};
```

runtime: O(n * m) where m is the length of the shortest string in the input