题目链接 ： https://leetcode.cn/problems/non-decreasing-subsequences/description/题目描述 ：class Solution {
public : vector< vector< int >> findSubsequences ( vector< int > & nums) { vector< vector< int >> ans; vector< int > path; int n = nums. size ( ) ; function< void ( int ) > dfs = [ & ] ( int i) -> void { if ( i == n) { if ( path. size ( ) > 1 ) { ans. emplace_back ( path) ; } return ; } if ( path. empty ( ) || nums[ i] != path. back ( ) ) { dfs ( i + 1 ) ; } if ( path. empty ( ) || nums[ i] >= path. back ( ) ) { path. push_back ( nums[ i] ) ; dfs ( i + 1 ) ; path. pop_back ( ) ; } } ; dfs ( 0 ) ; return ans; }
} ;
题目链接 ： https://leetcode.cn/problems/permutations/description/题目描述 ：class Solution {
public : vector< vector< int >> permute ( vector< int > & nums) { vector< vector< int >> ans; int n = nums. size ( ) ; vector< int > path ( n) ; function< void ( int ) > dfs = [ & ] ( int i) -> void { if ( i == n) { ans. emplace_back ( path) ; return ; } for ( int j = 0 ; j < n; j++ ) { if ( nums[ j] <= 10 ) { path[ i] = nums[ j] ; nums[ j] += 21 ; dfs ( i + 1 ) ; nums[ j] -= 21 ; } } } ; dfs ( 0 ) ; return ans; }
} ;
题目链接 ： https://leetcode.cn/problems/permutations-ii/description/题目描述 ：class Solution {
public : vector< vector< int >> permuteUnique ( vector< int > & nums) { vector< vector< int >> ans; int n = nums. size ( ) ; vector< int > path; ranges:: sort ( nums) ; vector< int > visited ( n) ; function< void ( int ) > dfs = [ & ] ( int i) -> void { if ( i == n) { ans. emplace_back ( path) ; return ; } for ( int j = 0 ; j < n; j++ ) { if ( visited[ j] || j > 0 && nums[ j] == nums[ j - 1 ] && ! visited[ j - 1 ] ) { continue ; } path. push_back ( nums[ j] ) ; visited[ j] = true ; dfs ( i + 1 ) ; visited[ j] = false ; path. pop_back ( ) ; } } ; dfs ( 0 ) ; return ans; }
} ;
题目链接 ： https://leetcode.cn/problems/reconstruct-itinerary/description/题目描述 ：class Solution {
public : vector< string> findItinerary ( vector< vector< string>> & tickets) { vector< string> ans = { "JFK" } ; unordered_map< string, map< string, int >> targets; for ( auto & ticket : tickets) { targets[ ticket[ 0 ] ] [ ticket[ 1 ] ] ++ ; } function< bool ( int ) > dfs = [ & ] ( int i) -> bool { if ( ans. size ( ) == i + 1 ) { return true ; } for ( auto & [ destination, cnt] : targets[ ans. back ( ) ] ) { if ( cnt > 0 ) { ans. push_back ( destination) ; cnt-- ; if ( dfs ( i) ) { return true ; } ans. pop_back ( ) ; cnt++ ; } } return false ; } ; dfs ( tickets. size ( ) ) ; return ans; }
} ;
题目链接 ： https://leetcode.cn/problems/n-queens/题目描述 ：class Solution {
public : vector< vector< string>> solveNQueens ( int n) { vector< vector< string>> ans; vector< int > columns ( n) ; vector< bool > on_path ( n) , diag1 ( 2 * n - 1 ) , diag2 ( 2 * n - 1 ) ; function< void ( int ) > dfs = [ & ] ( int r) -> void { if ( r == n) { vector< string> board ( n) ; for ( int i = 0 ; i < n; i++ ) { board[ i] = string ( columns[ i] , '.' ) + 'Q' + string ( n - 1 - columns[ i] , '.' ) ; } ans. emplace_back ( board) ; return ; } for ( int c = 0 ; c < n; c++ ) { int rc = r - c + n - 1 ; if ( ! on_path[ c] && ! diag1[ r + c] && ! diag2[ rc] ) { columns[ r] = c; on_path[ c] = diag1[ r + c] = diag2[ rc] = true ; dfs ( r + 1 ) ; on_path[ c] = diag1[ r + c] = diag2[ rc] = false ; } } } ; dfs ( 0 ) ; return ans; }
} ;
题目链接 ： https://leetcode.cn/problems/sudoku-solver/题目描述 ：class Solution {
public : void solveSudoku ( vector< vector< char >> & board) { vector< bitset< 9 >> rows ( 9 , bitset < 9 > ( ) ) ; vector< bitset< 9 >> columns ( 9 , bitset < 9 > ( ) ) ; vector< vector< bitset< 9 >> > cells ( 3 , vector < bitset< 9 >> ( 3 , bitset < 9 > ( ) ) ) ; function< bitset < 9 > ( int , int ) > getPossibleStatus = [ & ] ( int x, int y) -> bitset< 9 > { return ~ ( rows[ x] | columns[ y] | cells[ x / 3 ] [ y / 3 ] ) ; } ; function< vector < int > ( ) > getNext = [ & ] ( ) -> vector< int > { vector< int > ret; int minCnt = 10 ; for ( int i = 0 ; i < 9 ; i++ ) { for ( int j = 0 ; j < 9 ; j++ ) { if ( board[ i] [ j] != '.' ) { continue ; } auto cur = getPossibleStatus ( i, j) ; if ( cur. count ( ) >= minCnt) { continue ; } ret = { i, j} ; minCnt = cur. count ( ) ; } } return ret; } ; function< void ( int , int , int , bool ) > fillNum = [ & ] ( int x, int y, int n, bool fillFlag) -> void { rows[ x] [ n] = ( fillFlag) ? 1 : 0 ; columns[ y] [ n] = ( fillFlag) ? 1 : 0 ; cells[ x / 3 ] [ y / 3 ] [ n] = ( fillFlag) ? 1 : 0 ; } ; function< bool ( int ) > dfs = [ & ] ( int i) -> bool { if ( i == 0 ) { return true ; } auto next = getNext ( ) ; auto bits = getPossibleStatus ( next[ 0 ] , next[ 1 ] ) ; for ( int n = 0 ; n < bits. size ( ) ; n++ ) { if ( ! bits. test ( n) ) { continue ; } fillNum ( next[ 0 ] , next[ 1 ] , n, true ) ; board[ next[ 0 ] ] [ next[ 1 ] ] = n + '1' ; if ( dfs ( i - 1 ) ) { return true ; } board[ next[ 0 ] ] [ next[ 1 ] ] = '.' ; fillNum ( next[ 0 ] , next[ 1 ] , n, false ) ; } return false ; } ; int cnt = 0 ; for ( int i = 0 ; i < 9 ; i++ ) { for ( int j = 0 ; j < 9 ; j++ ) { cnt += ( board[ i] [ j] == '.' ) ; if ( board[ i] [ j] == '.' ) { continue ; } int n = board[ i] [ j] - '1' ; rows[ i] |= ( 1 << n) ; columns[ j] |= ( 1 << n) ; cells[ i / 3 ] [ j / 3 ] |= ( 1 << n) ; } } dfs ( cnt) ; }
} ;
