/**

 * @param {string[]} strs

 * @return {string}

 */

var longestCommonPrefix = function(strs) {

    let ans = "";

    let len = strs.length;

    for(let i = 0; strs[0][i]; ++i) {

        let ch = strs[0][i];

        if(!ch) return ans;

        for(let j = 1; j < len; ++j) {

            if(!strs[j][i] || strs[j][i] != ch) return ans;

        }    

        ans = ans+ch;

    }

    return ans

};

/**

 * @param {string} s

 * @return {number}

 */

var lengthOfLongestSubstring = function(s) {

    let len = s.length;

    if(len == 0) return 0;

    let m = new Map();

    let [l, r] = [0, 0];

    let ans = 0;

    while(r < len) {

        while(m.has(s[r]))    // 出现过

            m.delete(s[l++]);   // 删除最左边的元素 直至出现过的元素消失

        m.set(s[r], r);

        ++r;

        ans = Math.max(ans, r-l);

    }

    return ans;

};

/**

 * @param {TreeNode} root

 * @return {number}

 */

var maxPathSum = function(root) {

    let ans = -Infinity;

    var maxPath = function(root) {

        if(!root) return 0;

        let [lp, rp] = [Math.max(maxPath(root.left), 0), Math.max(maxPath(root.right), 0)];

        ans = Math.max(ans, lp+rp+root.val);

        return Math.max(lp, rp) + root.val;

    }

    maxPath(root)

    return ans;

};