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z algorithm

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	`1`	`+// Z-algorithm`
	`2`	`+// https://snuke.hatenablog.com/entry/2014/12/03/214243`
	`3`	`+// https://youtu.be/Uqtxz1KTKOQ?t=9214`
	`4`	`+struct Z {`
	`5`	`+ int n;`
	`6`	`+ string s;`
	`7`	`+ vector<int> z;`
	`8`	`+ Z() {}`
	`9`	`+ Z(const string& s): s(s) { init();}`
	`10`	`+ void init() {`
	`11`	`+ n = s.size();`
	`12`	`+ z = vector<int>(n);`
	`13`	`+ z[0] = n;`
	`14`	`+ for (int i = 1, j = 0; i < n;) {`
	`15`	`+ while (i+j < n && s[i+j] == s[j]) ++j;`
	`16`	`+ z[i] = j;`
	`17`	`+ if (j) {`
	`18`	`+ int k = 1;`
	`19`	`+ while (i+k < n && k+z[k] < j) {`
	`20`	`+ z[i+k] = z[k];`
	`21`	`+ k++;`
	`22`	`+ }`
	`23`	`+ i += k; j -= k;`
	`24`	`+ } else i++;`
	`25`	`+ }`
	`26`	`+ }`
	`27`	`+ int operator[](int i) const { return z[i];}`
	`28`	`+};`

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