Brute Force Algorithms: Push Button Lock and Zipper Problem Solutions, Study notes of Algorithms and Programming

Download Brute Force Algorithms: Push Button Lock and Zipper Problem Solutions and more Study notes Algorithms and Programming in PDF only on Docsity! COMP157 Fall 2007 brute force examples Sept. 17 Brute force solution to Push Button Lock: A Test is one possible assignment of buttons  combinations: Recursively build all possible button  combination assignments (including invalid ones). Check if a button  combination assignment is valid: struct Test { int x[11]; int n; Test(int _n) { n = _n; } Test(const Test& o) { n=o.n; for (int i=0; i<o.n; i++) x[i]=o.x[i]; } }; void make_tests(int n, int max, vector<Test>& v) { if (n==1) { for (int j=0; j<=max; j++) { Test t(1); t.x[0] = j; v.push_back(t); } return; } vector<Test> v2; make_tests(n-1,max,v2); for (unsigned int i=0; i<v2.size(); i++) { Test copy(v2[i]); copy.n++; for (int j=0; j<=max; j++) { copy.x[n-1]=j; v.push_back(copy); } } } bool checkTest(Test& test) { int combos[11]; int n = 0; int i; for (i=0; i<test.n; i++) if (test.x[i]<test.n) { combos[n] = test.x[i]; n++; } sort(combos, n); if (combos[0] != 0) return false; for (i=0; i<n-1; i++) if ((combos[i+1]-combos[i])>1) return false; return true; } COMP157 Fall 2007 brute force examples Sept. 17 Solve the problem for a specific number of buttons: Official judge’s solution to Push Button Lock (not brute force?): int solve(int num_buttons) { // make vector containing all possible assignments vector<Test> v; make_tests(num_buttons, num_buttons, v); // count the number of valid assignments int count = 0; for (unsigned int i=0; i<v.size(); i++) if (checkTest(v[i])) count++; return count; } unsigned int max_move = 0; int savemove[16384]; unsigned long count(unsigned int used) { unsigned int move; unsigned int nMove = 0; if(savemove[used] > 0){ return(savemove[used]); } for (move = 1; move < max_move; move++) { if (move & used) { continue; } nMove++; nMove += count(used | move); } savemove[used] = nMove; return(nMove); } int solve(int num_buttons) { max_move = 1<<num_buttons; // 2^n ::memset(&(savemove[0]), '\0', sizeof(savemove)); return count(0); }