[Joo kangsan] 24.11.26

[JooKangsan]

📌 푼 문제

문제이름	문제링크
Merge Intervals	https://leetcode.com/problems/merge-intervals
Min Cost to Connect all points	https://leetcode.com/problems/min-cost-to-connect-all-points
Lowest Common ancestor of a Binary Search Tree	https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree
Word Break	https://leetcode.com/problems/word-break
Kth largest element in an Array	https://leetcode.com/problems/kth-largest-element-in-an-array

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📝 간단한 풀이 과정

56. Merge Intervals

var merge = function (intervals) {
  intervals.sort((a, b) => a[0] - b[0]);

  for (let i = 1; i < intervals.length; i++) {
    if (intervals[i][0] <= intervals[i - 1][1]) {
      intervals[i][1] = Math.max(intervals[i][1], intervals[i - 1][1]);
      intervals[i][0] = intervals[i - 1][0];
      intervals.splice(i - 1, 1);
      i--;
    }
  }

  return intervals;
};

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1584. Min Cost to Connect all points

이문제는 결국 못풀어서 챗지피티한테 물어봐서 답을 얻고 이해하는데 시간을 쏟았습니다.

var minCostConnectPoints = function (points) {
  const n = points.length;
  const visited = new Array(n).fill(false);
  const minDist = new Array(n).fill(Infinity);
  minDist[0] = 0;
  let result = 0;
  for (let i = 0; i < n; i++) {
    let x = -1;
    for (let j = 0; j < n; j++) {
      if (!visited[j] && (x === -1 || minDist[j] < minDist[x])) {
        x = j;
      }
    }
    visited[x] = true;
    result += minDist[x];
    for (let k = 0; k < n; k++) {
      if (!visited[k]) {
        const dist =
          Math.abs(points[x][0] - points[k][0]) +
          Math.abs(points[x][1] - points[k][1]);
        minDist[k] = Math.min(minDist[k], dist);
      }
    }
  }
  return result;
};

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235. Lowest Common ancestor of a Binary Search Tree

var lowestCommonAncestor = function(root, p, q) {
  let min = Math.min(p.val, q.val)
  let max = Math.max(p.val, q.val)

  if(min > root.val) {
      return lowestCommonAncestor(root.right, p, q)
  } else if(max < root.val) {
      return lowestCommonAncestor(root.left, p, q)
  } else {
      return root
  }
};

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139. Word Break

var wordBreak = function(s, wordDict) {
    const memo = new Map();

    function dp(str, i = 0) {
        if (str.length === 0) return true;
        if (i >= wordDict.length) return false;

        const key = str + ',' + i;
        if (memo.has(key)) return memo.get(key);

        let word = wordDict[i];
        if (str.slice(0, word.length) === word) {
            if (dp(str.slice(word.length), 0)) {
                memo.set(key, true);
                return true;
            }
        }

        const result = dp(str, i + 1);
        memo.set(key, result);
        return result;
    }

    return dp(s);
};

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215. Kth largest element in an Array

var findKthLargest = function(nums, k) {
  let [min, max] = nums.reduce(([min, max], num) => 
      [Math.min(min, num), Math.max(max, num)], 
      [Infinity, -Infinity]
  );

  const offset = min >= 0 ? 0 : -min;
  const count = new Array(max + 1 + offset).fill(0);

  for(let num of nums) {
      count[num + offset]++;
  }

  let kthLargest;
  for(let i = count.length - 1; i >= 0; i--) {
      k -= count[i];
      if(k <= 0) {
          kthLargest = i - offset;
          break;
      }
  }

  return kthLargest;
};

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저번주부터 너무 어려워요.,..