The Recursive Backtracking Method of javascript solves the eight queens problem, and the javascript Recursion

The Recursive Backtracking Method of javascript solves the eight queens problem, and the javascript Recursion

Next I will share with you the solution of the eight queens by the backtracing method, with detailed annotations. There is not much nonsense here.

Function NQueens (order) {if (order <4) {console. log ('n Queens problem apply for order bigger than 3! '); Return;} var nQueens = []; var backTracking = false; rowLoop: for (var row = 0; row <order; row ++) {// if row is smaller than 0, the problem is not solved. if (row <0) {console. log ('this N Queens problem has no solution! '); Break;} // The first time a new row is detected, if (nQueens [row] === undefined) {nQueens [row] = [];} // program block for (var col = 0; col <order; col ++) {// 0 indicates the location where the queen has been detected and placed. if (nQueens [row] [col] = 0) {continue;} // during backtracking, when the location where the queen can be placed is displayed, it indicates that this location has not passed the verification. You need to re-process else if (backTracking & nQueens [row] [col] = 1) {// when backtracking, it is found that the last row ends at the end of the row. You need to continue backtracking if (col = order-1) {resetRow (nQueens, order, row ); row = row-2; continue rowLoop;} // return The traced row has not reached the end of the row. Mark it as 0. continue nQueens [row] [col] = 0; backTracking = false; continue ;} // place a queen nQueens [row] [col] = 1; // locate a location where the queen can be placed and jump out to the next line (only one queen can be placed on one line ). If (isQueenValid (nQueens, row, col) {continue rowLoop;} // each row should have a queen. No proper position is found at the end of the column, it indicates that there is a problem with the placement of the queen. You need to trace back! Else if (col = order-1) {backTracking = true; // both 0 and 1 indicate that this position has been detected. Therefore, we need to clear the row as undefined resetRow (nQueens, order, row); // minus 2 because there is an auto-increment at the end of the loop, which is actually returning to the previous row = row-2; // returns to the outer loop and continues to continue rowLoop ;} else {// The nQueens [row] [col] = 0; continue ;}}return nQueens;} // before backtracking, clear the row function resetRow (nQueens, order, row) {for (var col = 0; col <order; col ++) {nQueens [row] [col] = undefined;} // check whether the position can be placed in the Queen's function isQueenValid (nQueens, row, col) {// row detection for (var I = 0; I <col; I ++) {if (nQueens [row] [I] = 1) {return false ;}} for (var j = 1; j <row + 1; j ++) {// check the upper left 45 degrees and upper right 45 degrees if (nQueens [row-j] [col] = 1 | (nQueens [row-j] [col-j] = = 1) | (nQueens [row-j] [col + j] = 1) {return false ;}} return true ;} function printQ (queens) {for (var row = 0; row <queens. length; row ++) {var rowText = ''; for (var col = 0; col <queens. length; col ++) {if (queens [row] [col] === undefined) {queens [row] [col] = 0 ;} rowText = rowText + queens [row] [col] + '';} console. log (rowText) ;}}var queens = NQueens (8); printQ (queens );

The above is all the content of this article. I hope you will like it.