发现数据结构之美-栈 #208
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什么是栈？
数据结构图
入栈出栈图
JavaScript中的栈在js中，如何发现出栈LIFO的特性？下面这个结构大家都熟悉，瞬间体现出栈LIFO的特性。 // 定义一个栈
let stack = [1,2,3];
// 入栈
stack.push(4); // stack [1,2,3,4]
// 出栈
stack.pop(); // 4 stack [1,2,3]如何实现一个最小栈？设计一个支持 push ，pop ，top 操作，并能在常数时间内检索到最小元素的栈。 var MinStack = function() {
this.stack = [];
};
MinStack.prototype.push = function(x) {
this.stack.push(x);
};
MinStack.prototype.pop = function() {
return this.stack.pop();
};
MinStack.prototype.top = function() {
return this.stack[this.stack.length - 1];
};
MinStack.prototype.getMin = function() {
return Math.min(...this.stack);
};题目：https://leetcode-cn.com/problems/min-stack/ 图解函数调用栈
从frames stack中调用函数。 function foo(){
let a = 10;
return a + b + 11
}
function bar(x){
let y = 3;
return foo(x*y);
}
console.log(bar(7)); // 返回42过程拆解：
可视化拆解：
|
leetcode 栈 解法题目
20.有效的括号（easy）题目：https://leetcode-cn.com/problems/valid-parentheses/ /**
* 解法2：栈
* 1.构建一个栈
* 2.依次入栈所有开括号
* 3.遇到闭括号时与栈顶的开括号匹配
* 3.1若匹配上，出栈并继续
* 3.2匹配不上，return false
* 4.遍历结束后的栈应该为空，否则为无效括号
*/
var isValid = function(s) {
var bracketsMap = {
"(": ")",
"{": "}",
"[": "]"
};
var openBrackets = Object.keys(bracketsMap);
var closeBrackets = Object.values(bracketsMap);
var stack = [];
var sArr = s.split("");
for (var i = 0; i < sArr.length; i++) {
if (openBrackets.indexOf(sArr[i]) !== -1) {
stack.push(sArr[i]);
} else if (closeBrackets.indexOf(sArr[i]) !== -1) {
var top = stack[stack.length - 1];
if (sArr[i] === bracketsMap[top]) {
stack.pop();
} else {
return false;
}
}
}
return stack.length === 0;
}67.二进制求和（easy）/**
* @param {string} a
* @param {string} b
* @return {string}
*/
var addBinary = function (a, b) {
/**
* 解法2：栈
* 时间复杂度：O(n)
* 性能：56ms, 35.5MB
*/
let aArr = a.split("");
let bArr = b.split("");
let stack = [];
let count = 0;
while (aArr.length !== 0 || bArr.length !== 0) {
let aPop = aArr.pop() || 0;
let bPop = bArr.pop() || 0;
let stackBottom = 0;
if (stack.length > count) {
stackBottom = stack.shift() || 0;
}
let sum = parseInt(aPop) + parseInt(bPop) + parseInt(stackBottom)
if (sum <= 1) {
stack.unshift(sum);
} else {
stack.unshift(sum - 2);
stack.unshift(1);
}
count++;
}
return stack.join("");
};905.按奇偶排序数组（easy）题目：https://leetcode-cn.com/problems/sort-array-by-parity/ /**
* @param {number[]} A
* @return {number[]}
*/
var sortArrayByParity = function (A) {
/**
* 栈头栈尾解法即可
* 偶数栈底推入unshift
* 奇数栈顶推入push
*/
var stack = [];
for (var i = 0; i < A.length; i++) {
if (A[i] % 2 === 0) {
stack.unshift(A[i]);
} else {
stack.push(A[i]);
}
}
return stack;
};56.合并区间（medium）题目：https://leetcode-cn.com/problems/merge-intervals/ /**
* @param {number[][]} intervals
* @return {number[][]}
*/
var merge = function (intervals) {
/**
* 解法1：排序 + 栈
* 性能：88ms 36.3MB
* 思路：
* 推入区间 空栈 或者 arr[0]大于栈最后一个区间闭
* 覆盖重叠 arr[0]小于栈最后一个区间闭
* */
intervals.sort((a, b) => a[0] - b[0]);
let stack = [];
for (let i = 0; i < intervals.length; i++) {
let currrentInterval = intervals[i];
let stackLastItem = stack[stack.length - 1];
if (stack.length === 0 || currrentInterval[0] > stackLastItem[1]) {
stack.push(currrentInterval);
} else if (currrentInterval[0] <= stackLastItem[1]) {
stackLastItem[1] = Math.max(stackLastItem[1], currrentInterval[1]);
}
}
return stack;
};75. 颜色分类（medium）题目：https://leetcode-cn.com/problems/sort-colors/ var sortColors = function (nums) {
/**
* 解法1：递归 栈
* 性能：64ms 35.1MB
*/
var length = nums.length;
var countHead = arguments[1] || 0;
var countTail = arguments[2] || 0;
for (var i = countHead || 0; i < length - countTail; i++) {
if (nums[i] === 0) {
countHead++;
nums.unshift(nums.splice(i, 1)); // 增加if(i!==0)会降低10ms性能
return sortColors(nums, countHead, countTail);
} else if (nums[i] === 2) {
countTail++;
nums.push(nums.splice(i, 1));
return sortColors(nums, countHead, countTail);
}
}
return nums;
}228.汇总区间（medium）题目：https://leetcode-cn.com/problems/summary-ranges/ /**
* @param {number[]} nums
* @return {string[]}
*/
var summaryRanges = function (nums) {
/**
* 解法1：排序 + 栈
* 性能：52ms 33.7MB
*/
nums.sort((a, b) => a - b);
let stack = [];
let result = [];
for (let i = 0; i < nums.length; i++) {
if (stack.length === 0 || nums[i] - stack[stack.length - 1] === 1) {
stack.push(nums[i]);
} else {
stackToResult();
stack = [];
stack.push(nums[i]);
}
if (i === nums.length - 1) {
stackToResult();
}
}
function stackToResult() {
if (stack.length > 1) {
result.push(`${stack[0]}->${stack[stack.length - 1]}`);
} else {
result.push(`${stack[0]}`);
}
}
return result;
};739.每日温度（medium）题目：https://leetcode-cn.com/problems/daily-temperatures/ /**
* 解法2：栈 + 递归 1132ms 19.96% 59.2MB 11.76%
* 思路：
* 1.通过shift取出栈底元素
* 2.遍历剩余温度栈内温度
* 若温度出现比栈底温度大者
* 存储i+1
* 递归进行下一次入栈
* 若温度小于等于栈底温度
* 若遍历到最后一个都没有出现更大的
* 存储 0
* 进行下一次入栈
* 3.最后一个温度无论如何都肯定是0
*/
var dailyTemperatures = function(T) {
if (T.length < 1 || T.length > 30000) return false;
var result = arguments[1] || [];
var bottom = T.shift();
for (var i = 0; i < T.length; i++) {
var t = T[i];
if (t > bottom) {
result.push(i + 1);
return dailyTemperatures(T, result);
} else {
if (i === T.length - 1) {
result.push(0);
return dailyTemperatures(T, result);
}
}
}
result.push(0);
return result;
} |
面试题 栈 解法题目实现一个BigInt实现大整数相加，大于 Number.MAX_VALUE，不能直接使用 BigInt。 /**
* 请通过代码实现大整数（可能比Number.MAX_VALUE大）相加运算
// your code goes here
var bigint1 = new BigInt('1231230');
var bigint2 = new BigInt('12323123999999999999999999999999999999999999999999999991');
console.log(bigint1.plus(bigint2))
*/function BigInt(value) {
this.value = value;
}
BigInt.prototype.plus = function (bigint) {
let aArr = this.value.split("");
let bArr = bigint.value.split("");
let stack = [];
let count = 0;
while (aArr.length !== 0 || bArr.length !== 0) {
let aPop = aArr.pop() || 0;
let bPop = bArr.pop() || 0;
let stackBottom = 0;
if (stack.length > count) {
stackBottom = stack.shift();
}
let sum = parseInt(aPop) + parseInt(bPop) + parseInt(stackBottom);
if (sum < 10) {
stack.unshift(sum);
} else if (sum >= 10) {
stack.unshift(sum - 10);
stack.unshift(1);
}
count++;
}
return stack.join("");
}; |
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这篇博文非常适合数据结构基础非常薄弱的同学食用，也欢迎基础扎实的同学指正和交流。
如果从未感受过stack的美妙和强大，这篇博文将非常适合你~
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