[krokerdile] WEEK 03 solutions

combination-sum/krokerdile.js

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+/**
+ * @param {number[]} candidates
+ * @param {number} target
+ * @return {number[][]}
+ */
+var combinationSum = function(candidates, target) {
+    const result = [];
+
+    const dfs = (start, path, sum) => {
+        if (sum === target) {
+            result.push([...path]); // 정답 조합 발견
+            return;
+        }
+
+        if (sum > target) return; // target 초과 -> 백트랙
+
+        for (let i = start; i < candidates.length; i++) {
+            path.push(candidates[i]);        // 숫자 선택
+            dfs(i, path, sum + candidates[i]); // 같은 인덱스부터 다시 탐색 (중복 사용 허용)
+            path.pop();                      // 백트래킹
+        }
+    };
+
+    dfs(0, [], 0);
+    return result;
+};

decode-ways/krokerdile.js

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+/**
+ * @param {string} s
+ * @return {number}
+ */
+var numDecodings = function(s) {
+    const n = s.length;
+    const memo = {};
+
+    function dfs(index) {
+        if (index === n) return 1;
+        if (s[index] === '0') return 0;
+        if (memo.hasOwnProperty(index)) return memo[index];
+
+        let count = dfs(index + 1);
+        if (index + 1 < n) {
+            const twoDigit = parseInt(s.slice(index, index + 2));
+            if (twoDigit >= 10 && twoDigit <= 26) {
+                count += dfs(index + 2);
+            }
+        }
+
+        memo[index] = count;
+        return count;
+    }
+
+    return dfs(0);
+};

maximum-subarray/krokerdile.js

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+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var maxSubArray = function(nums) {
+    let maxSum = nums[0];
+    let currentSum = nums[0];
+
+    for (let i = 1; i < nums.length; i++) {
+        // 지금 원소 자체가 더 클 수도 있음 (부분합 리셋)
+        currentSum = Math.max(nums[i], currentSum + nums[i]);
+        maxSum = Math.max(maxSum, currentSum);
+    }
+
+    return maxSum;
+};

number-of-1-bits/krokerdile.js

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+/**
+ * @param {number} n
+ * @return {number}
+ */
+var hammingWeight = function(n) {
+    let list = n.toString(2).split('').map(Number);
+    let sum = 0;
+    list.forEach((m)=>{
+        if(m == 1){
+            sum += 1;a
+        }
+    })
+    return sum;
+};

valid-palindrome/krokerdile.js

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+function filterStr(inputString) {
+    return inputString.replace(/[^a-zA-Z0-9]/g, '').toLowerCase();
+}
+
+var isPalindrome = function(s) {
+    const filtered = filterStr(s);
+    const reversed = filtered.split('').reverse().join('');
+    return filtered === reversed;
+};