题解 | #最小覆盖子串#

/**
  * 
  * @param S string字符串 
  * @param T string字符串 
  * @return string字符串
  */
function minWindow( s ,  t ) {
    // write code here
    const needMap = new Map()
    for (const char of t) {
        needMap.set(char, needMap.get(char) + 1 || 1)
    }
    const targetLength = needMap.size
    const matchMap = new Map()
    let match = 0
    let res = ''
    let i = 0
    let j = 0
    while (j < s.length) {
        let char = s[j]
        if (needMap.has(char)) {
            matchMap.set(char, matchMap.get(char) + 1 || 1)
            if (needMap.get(char) === matchMap.get(char)) {
                match++
            }
        }
        while (match === targetLength) {
            if (!res || res.length > (j - i + 1)) {
                res = s.slice(i, j + 1)
            }
            i++
            const lastChar = s[i - 1]
            if (matchMap.has(lastChar)) {
                matchMap.set(lastChar, matchMap.get(lastChar) - 1)
                if (matchMap.get(lastChar) < needMap.get(lastChar)) {
                    match--
                }
            }
        }
        j++
    }
    return res
    
}
module.exports = {
    minWindow : minWindow
};