/**
* @param {string} s1
* @param {string} s2
* @return {boolean}
*/
var areAlmostEqual = function(s1, s2) {
let idx = []
for(let i=0; i<s1.length; i++) {
if(s1[i] !== s2[i]) idx.push(i)
}
return idx.length === 2 && s1[idx[0]] === s2[idx[1]] && s1[idx[1]] === s2[idx[0]] || idx.length === 0 ? true : false
};