chore: some algs

Author: ceilf6

JS/algorithm/bigInt.js

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+/**
+ * 
+ * @param {string} a 
+ * @param {string} b 
+ * @returns 
+ */
+function addBigNumber(a, b) {
+    let i = a.length - 1;
+    let j = b.length - 1;
+    let carry = 0; // 进位信息
+    // 如果用数组进行管理还复杂化了，不如直接设一个变量存储进位信息
+    let res = "";
+
+    while (i >= 0 || j >= 0 || carry > 0) {
+        const x = i >= 0 ? a[i] - '0' : 0; // >=0 实现越界处理
+        const y = j >= 0 ? b[j] - '0' : 0;
+
+        const sum = x + y + carry;
+        res = (sum % 10) + res;
+        carry = Math.floor(sum / 10);
+
+        i--;
+        j--;
+    }
+
+    return res;
+}
+console.log(addBigNumber('1111111111111111', '22222222222222222222'))
+
+function multiplyBigNumber(num1, num2) {
+    if (num1 === "0" || num2 === "0") return "0";
+
+    const m = num1.length;
+    const n = num2.length;
+    const res = new Array(m + n).fill(0);
+    // num1[i] * num2[j] 的结果会落在结果数组的 i + j 和 i + j + 1 位置
+
+    // O(m*n)
+    for (let i = m - 1; i >= 0; i--) {
+        for (let j = n - 1; j >= 0; j--) {
+            const x = num1.charCodeAt(i) - 48; // num1[i] - 48
+            const y = num2.charCodeAt(j) - 48;
+
+            const mul = x * y;
+            const p1 = i + j;
+            const p2 = i + j + 1;
+
+            const sum = mul + res[p2];
+            res[p2] = sum % 10;
+            res[p1] += Math.floor(sum / 10);
+        }
+    }
+
+    let start = 0;
+    while (start < res.length && res[start] === 0) {
+        start++;
+    }
+
+    return res.slice(start).join("");
+}

JS/algorithm/cacheStairs.js

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+function solve(n) {
+    const ans = []
+    const cur = []
+
+    // 求路径的话不适合回溯，面试官说错了
+    function dfs(step) {
+        if (step < 0) return
+
+        if (step === 0) {
+            ans.push([...cur])
+            return
+        }
+
+        cur.push(1)
+        dfs(step - 1)
+        cur.pop()
+
+        cur.push(2)
+        dfs(step - 2)
+        cur.pop()
+    }
+
+    dfs(n)
+    return ans
+}

JS/algorithm/thousands.ts

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+// toLocaleString 原生API
+function localeAPI(num: number): string {
+    return num.toLocaleString()
+}
+console.log(localeAPI(1234567890))
+
+
+function formatThousands(num) {
+    const str = String(num)
+    const [intPart, decimalPart] = str.split('.')
+    // 小数处理
+
+    let res = ''
+    let count = 0
+
+    for (let i = intPart.length - 1; i >= 0; i--) {
+        res = intPart[i] + res
+        count++
+
+        if (count % 3 === 0 && i !== 0) {
+            res = ',' + res
+        }
+    }
+
+    return decimalPart !== undefined ? res + '.' + decimalPart : res
+}
+
+console.log(formatThousands(1234567890)) // 1,234,567,890
+console.log(formatThousands(1234567.89)) // 1,234,567.89