week2알고리즘

deleteDuplicates.js

function ListNode(val, next) {
    this.val = (val === undefined ? 0 : val)
    this.next = (next === undefined ? null : next)
}

var deleteDuplicates = function (head) {
    let curr = head;
  
    //head and next exist
    while (curr !== null && curr.next !== null) {
        if (curr.val === curr.next.val) {
            curr.next = curr.next.next;
        } else {
            curr = curr.next;
        };
    }
    return head;
}

hasCycle.js

var hasCycle = function (head) {
    let fastOne = head;
    let slowOne = head;

    while (fastOne !== null && fastOne.next !== null) {
        fastOne = fastOne.next.next;
        slowOne = slowOne.next;
        if (fastOne === slowOne) {
            return true;
        }
    }
    return false;
};

longestCommon.js

var longestCommonPrefix = function (strs) {
    let answer = '';
    //no value
    if (strs.length === 0) {
        return answer;
    }
    //1개의 prefix
    if (strs.length === 1) {
        answer += strs;
        return answer;
    }

    //여러 prefix 중 제일 짧은 것
    strs.sort((a, b) => a.length - b.length);
    shortstrs = strs[0].split("");

    for (let str of strs) {
        for (let i = 0; i < shortstrs.length; i++) {
            if (str[i] === (shortstrs[i])) {
                answer += shortstrs[i];
            } else {
                break;
            }
        }
        answer += '/';
    }
    answer = answer.split('/');
    answer.sort((a, b) => a.length - b.length);
    return answer[1]
}

palindrome.js

var isPalindrome = function (x) {
    let answer = true;
    x = String(x);
    let middle = Math.floor(x.length / 2); //중간값

    for (let i = 0; i < middle; i++) {
        if (x[i] !== x[x.length - 1 - i]) {
            return false
        } else {
            answer = true;
        }
    }
    return answer;
};

let x = -1221;
console.log(isPalindrome(x))

reverseInteger.js

let x = -123;

var reverse = function (x) {
    let answer = [];
    let splicedX;
    x = String(x).split("")

    if (x[0] === '-') {
        splicedX = x.splice(0, 1);
    }

    for (let i of x) {
        answer.unshift(i);
    }

    if (splicedX) {
        answer.unshift(splicedX);
    }
    answer = parseInt(answer.join(''));
    return ((-(2 ** 31) <= answer) && (answer <= 2 ** 31 - 1)) ? answer : 0;
};


console.log(reverse(x))

twoSum.js

var twoSum = function (nums, target) {
    let sum = 0;
    for (let i = 0; i < nums.length - 1; i++) {
        for (let j = i + 1; j < nums.length; j++) {
            sum = nums[i] + nums[j];
            if (sum === target) {
                return [i, j];
            }
        }
    }
}