描述

• input S： ‘helloworld’ T: ‘dlr’
• output True or False

def checkInclusion(S: str, T: str) -> bool:
    need: dict[str:int] = {}
    window: dict[str:int] = {}
    flag: int = 0
    for c in T:
        need[c] = need.get(c, 0) + 1
    left: int = 0
    right: int = 0
    while right < len(S):
        c: str = S[right]
        right += 1
        if c in T:
            window[c] = window.get(c, 0) + 1
            if window[c] == need[c]:
                flag += 1
        # 当flag满足条件时候， 目标串可能出现
        while flag == len(need):
            if right - left == len(T): # [left, right], 这是当前窗口状态
                return True
            c = S[left]
            if c in T:
                if window[c] == need[c]:
                    flag -= 1
                window[c] -= 1
            left += 1
    return False
print(checkInclusion('w321ww', '231'))