Jun 18, 2022 · May 21, 2022 · May 21, 2022 · May 21, 2022 · Jun 16, 2022 · Jun 16, 2022
diff --git a/problems/0647.回文子串.md b/problems/0647.回文子串.md
Original file line number	Diff line number	Diff line change
Expand Up		@@ -406,6 +406,63 @@ const countSubstrings = (s) => {
		}
		```

	TypeScript:

	> 动态规划:

	```typescript
	function countSubstrings(s: string): number {
	/**
	dp[i][j]: [i,j]区间内的字符串是否为回文(左闭右闭)
	*/
	const length: number = s.length;
	const dp: boolean[][] = new Array(length).fill(0)
	.map(_ => new Array(length).fill(false));
	let resCount: number = 0;
	// 自下而上,自左向右遍历
	for (let i = length - 1; i >= 0; i--) {
	for (let j = i; j < length; j++) {
	if (
	s[i] === s[j] &&
	(j - i <= 1 \|\| dp[i + 1][j - 1] === true)
	) {
	dp[i][j] = true;
	resCount++;
	}
	}
	}
	return resCount;
	};
	```

	> 双指针法:

	```typescript
	function countSubstrings(s: string): number {
	const length: number = s.length;
	let resCount: number = 0;
	for (let i = 0; i < length; i++) {
	resCount += expandRange(s, i, i);
	resCount += expandRange(s, i, i + 1);
	}
	return resCount;
	};
	function expandRange(s: string, left: number, right: number): number {
	let palindromeNum: number = 0;
	while (
	left >= 0 && right < s.length &&
	s[left] === s[right]
	) {
	palindromeNum++;
	left--;
	right++;
	}
	return palindromeNum;
	}
	```




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