2822-InversionOfObject.js

// 2822. Inversion of Object
// Given an object or an array obj, return an inverted object or array invertedObj.
// The invertedObj should have the keys of obj as values and the values of obj as keys. 
// The indices of array should be treated as keys. It is guaranteed that the values in obj are only strings. 
// The function should handle duplicates, meaning that if there are multiple keys in obj with the same value, the invertedObj should map the value to an array containing all corresponding keys.

// Example 1:
// Input: obj = {"a": "1", "b": "2", "c": "3", "d": "4"}
// Output: invertedObj = {"1": "a", "2": "b", "3": "c", "4": "d"}
// Explanation: The keys from obj become the values in invertedObj, and the values from obj become the keys in invertedObj.

// Example 2:
// Input: obj = {"a": "1", "b": "2", "c": "2", "d": "4"}
// Output: invertedObj = {"1": "a", "2": ["b", "c"], "4": "d"}
// Explanation: There are two keys in obj with the same value, the invertedObj mapped the value to an array containing all corresponding keys.

// Example 3:
// Input: obj = ["1", "2", "3", "4"]
// Output: invertedObj = {"1": "0", "2": "1", "3": "2", "4": "3"}
// Explanation: Arrays are also objects therefore array has changed to an object and the keys (indices) from obj become the values in invertedObj, and the values from obj become the keys in invertedObj.

// Constraints:
//         obj is a valid JSON object or array
//         typeof obj[key] === "string"
//         2 <= JSON.stringify(obj).length <= 10^5

/**
 * @param {Object|Array} obj
 * @return {Object}
 */
var invertObject = function(obj) {
    let res = {};
    for( o in obj ) {
        // 如果存在 要做数组化处理
        if(res[obj[o]] !== undefined) {
            // 如果已经是数组，追加即可
            if(Array.isArray(res[obj[o]])) {
                res[obj[o]].push(o)
            } else {
                res[obj[o]] = [res[obj[o]], o]
            }
        } else {
            res[obj[o]] = o;
        }
    }
    return res
};


console.log(invertObject({"a": "1", "b": "2", "c": "3", "d": "4"})) // {"1": "a", "2": "b", "3": "c", "4": "d"}
console.log(invertObject(["1", "2", "3", "4"])) // {"1": "0", "2": "1", "3": "2", "4": "3"}
console.log(invertObject({"a": "1", "b": "2", "c": "2", "d": "4"})) // {"1": "a", "2": ["b", "c"], "4": "d"}