置換->互換の積

decompose.js

// function decompose(l, i) {
//     if (i < l.length) {
//         var j = l[i]
//         if (i === j) {
//             return decompose(l, i + 1)
//         } else {
//             [l[i], l[j]] = [l[j], l[i]]
//             return [[i, j]].concat(decompose(l, i + 1))
//         }
//     } else {
//         return []
//     }
// }

function decompose(l) {
    let arr = []
    for (let i = 0; i < l.length; i++) {
        let j = l[i]
        if (i === j) continue
        [l[i], l[j]] = [l[j], l[i]]
        arr.push([i, j])
    }
    return arr
}


console.log(decompose([4, 5, 1, 2, 0, 3]))