leetcode - permutations.js

permutations.js

/**
 * @param {number[]} nums
 * @return {number[][]}
 */
function swap(nums, i, j) {
    let temp = nums[i]
    nums[i] = nums[j]
    nums[j] = temp
}
const indent = (length) => {
    let str = ""
    for(let i =0; i<length; i++) {
        str +="    "
    }
    return str
}
const permuteHelper = (nums, chosen, answer) => {
    // console.log(indent(chosen.length), "PermuteHelper", nums, '    ', chosen, '    ', answer)
    if(nums.length === 0) {
        answer.push(chosen)
            // console.log(indent(chosen.length), "***PermuteHelper", nums, '    ', chosen, '    ', answer)

        return 
    } else {
        for(let i =0; i<nums.length; i++) {
            // choose
            chosen.push(nums[i])
            // remove and explore
            let removed = nums.splice(i,1)
            permuteHelper(nums, [...chosen], answer)
            
            // un-choose. 
            nums.splice(i,0, ...removed)

            chosen.pop()
        }
    }
}
var permute = function(nums) {
    let answer = []
    permuteHelper(nums, [], answer)
    // console.log(answer)
    return answer
    // console.log("inside  permute", nums)
    // for(let i =0; i<nums.length - 1; i++) {
    //     swap(nums, i, i+1)
    //     console.log("after swap", nums)
    //     permute(nums)
    //     swap(nums, i, i+1)
    // }
};

// level 0
// 1,2,3

// level 1

// i=0
// 2,1,3
// 3,2,1

// i=1
// 1,3,2

// i=2

// level 2
// i=0
// 1,2,3
// 3,1,2

// i=1
// 3,1,2
// 2,3,1

// i=2