20. 有效的括号

function isValid(s: string): boolean {
    if (s.length % 2 === 1) {
        return false;
    };
    const map = {
        '(': ')',
        '[': ']',
        '{': '}',
    };
    const stack = [];
    for (let i = 0; i < s.length; i++) {
        if (s[i] === '(' || s[i] === '{' || s[i] === '[') {
            stack.push(map[s[i]]);
        } else {
            let popStr = stack.pop();
            if (popStr !== s[i]) {
                return false;
            }
        };
    }
    return stack.length === 0;
};

1047. 删除字符串中的所有相邻重复项

function removeDuplicates(s: string): string {
    const stack = [];
    for (let i = 0; i < s.length; i++) {
        let popValue = stack.pop();
        if (popValue !== s[i]) {
            stack.push(popValue);
            stack.push(s[i]);
        }
    };
    return stack.join('');
};

150. 逆波兰表达式求值

function evalRPN(tokens: string[]): number {
    const stack = [];
    for (let value of tokens) {
        if (value === '+' || value === '-' || value === '*' || value === '/') {
            const popValueOne = stack.pop();
            const popValueTwo = stack.pop();
            if (value === '+') {
                stack.push(popValueTwo + popValueOne);
            }
            if (value === '-') {
                stack.push(popValueTwo - popValueOne);
            }
            if (value === '*') {
                stack.push(popValueTwo * popValueOne);
            }
            if (value === '/') {
                stack.push(popValueTwo / popValueOne | 0);
            }
        } else {
            stack.push(Number(value));
        }
    }
    return stack[0];
};