[JangAyeon] WEEK 03 Solutions

combination-sum/JangAyeon.js

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+/**
+ * @param {number[]} candidates
+ * @param {number} target
+ * @return {number[][]}
+ */
+var combinationSum = function (arr, target) {
+  const N = arr.length;
+  const answer = [];
+  function dfs(total, idx, route) {
+    if (total >= target) {
+      if (total == target) {
+        answer.push(route);
+      }
+      return;
+    }
+    for (let i = idx; i < N; i++) {
+      dfs(total + arr[i], i, [...route, arr[i]]);
+    }
+  }
+
+  dfs(0, 0, []);
+  return answer;
+};

decode-ways/JangAyeon.js

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+var numDecodings = function (s) {
+  const N = s.length;
+  const memo = {};
+
+  function dfs(i) {
+    if (i === N) return 1;
+    if (s[i] === "0") return 0; // 0은 단독으로 decode 불가능
+    if (memo[i] !== undefined) return memo[i];
+
+    // 1자리
+    let count = dfs(i + 1);
+
+    // 2자리
+    if (i + 1 < N && Number(s.slice(i, i + 2)) <= 26) {
+      count += dfs(i + 2);
+    }
+
+    memo[i] = count;
+    return count;
+  }
+
+  return dfs(0);
+};

maximum-subarray/JangAyeon.js

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+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var maxSubArray = function (nums) {
+  let pointer = nums[0];
+  let answer = pointer;
+  const N = nums.length;
+  for (let idx = 1; idx < N; idx++) {
+    if (nums[idx] > pointer + nums[idx]) {
+      pointer = nums[idx];
+    } else {
+      pointer += nums[idx];
+    }
+    // console.log(idx, pointer)
+    answer = Math.max(pointer, answer);
+  }
+  return answer;
+};

number-of-1-bits/JangAyeon.js

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+/**
+ * @param {number} n
+ * @return {number}
+ */
+var hammingWeight = function (n) {
+  function calDivision(num) {
+    return { v: Math.floor(num / 2), rest: num % 2 };
+  }
+  let num = n;
+  let result = 0;
+  while (true) {
+    const { v, rest } = calDivision(num);
+    result += rest;
+    if (v == 0) {
+      break;
+    }
+    num = v;
+  }
+
+  return result;
+};

valid-palindrome/JangAyeon.js

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+/**
+ * @param {string} s
+ * @return {boolean}
+ */
+var isPalindrome = function (s) {
+  const sLowered = [...s.toLowerCase().replace(" ", "")];
+  const isAlpha = (item) => item.charCodeAt() >= 97 && item.charCodeAt() <= 122;
+  const isNumber = (item) => item.charCodeAt() >= 48 && item.charCodeAt() <= 57;
+  const str = sLowered.filter((c) => isAlpha(c) || isNumber(c));
+  const N = str.length;
+  let [start, end] = [0, N - 1];
+  while (start <= end) {
+    if (str[start] != str[end]) {
+      return false;
+    }
+    start++;
+    end--;
+  }
+  return true;
+};