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Merge pull request youngyangyang04#1378 from xiaofei-2020/dp52

添加(0647.回文子串.md):增加typescript版本

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- 0647.回文子串.md

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`@@ -406,6 +406,63 @@ const countSubstrings = (s) => {`
`406`	`406`	`}`
`407`	`407`	```
`408`	`408`
	`409`	`+TypeScript:`
	`410`	`+`
	`411`	`+> 动态规划:`
	`412`	`+`
	`413`	+```typescript
	`414`	`+function countSubstrings(s: string): number {`
	`415`	`+ /**`
	`416`	`+ dp[i][j]: [i,j]区间内的字符串是否为回文(左闭右闭)`
	`417`	`+ */`
	`418`	`+ const length: number = s.length;`
	`419`	`+ const dp: boolean[][] = new Array(length).fill(0)`
	`420`	`+ .map(_ => new Array(length).fill(false));`
	`421`	`+ let resCount: number = 0;`
	`422`	`+ // 自下而上,自左向右遍历`
	`423`	`+ for (let i = length - 1; i >= 0; i--) {`
	`424`	`+ for (let j = i; j < length; j++) {`
	`425`	`+ if (`
	`426`	`+ s[i] === s[j] &&`
	`427`	`+ (j - i <= 1 \|\| dp[i + 1][j - 1] === true)`
	`428`	`+ ) {`
	`429`	`+ dp[i][j] = true;`
	`430`	`+ resCount++;`
	`431`	`+ }`
	`432`	`+ }`
	`433`	`+ }`
	`434`	`+ return resCount;`
	`435`	`+};`
	`436`	+```
	`437`	`+`
	`438`	`+> 双指针法:`
	`439`	`+`
	`440`	+```typescript
	`441`	`+function countSubstrings(s: string): number {`
	`442`	`+ const length: number = s.length;`
	`443`	`+ let resCount: number = 0;`
	`444`	`+ for (let i = 0; i < length; i++) {`
	`445`	`+ resCount += expandRange(s, i, i);`
	`446`	`+ resCount += expandRange(s, i, i + 1);`
	`447`	`+ }`
	`448`	`+ return resCount;`
	`449`	`+};`
	`450`	`+function expandRange(s: string, left: number, right: number): number {`
	`451`	`+ let palindromeNum: number = 0;`
	`452`	`+ while (`
	`453`	`+ left >= 0 && right < s.length &&`
	`454`	`+ s[left] === s[right]`
	`455`	`+ ) {`
	`456`	`+ palindromeNum++;`
	`457`	`+ left--;`
	`458`	`+ right++;`
	`459`	`+ }`
	`460`	`+ return palindromeNum;`
	`461`	`+}`
	`462`	+```
	`463`	`+`
	`464`	`+`
	`465`	`+`
`409`	`466`
`410`	`467`	`-----------------------`
`411`	`468`	`<div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>`

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