function check1(arr, n) {
  for(var i = 0; i < n; i++) {
    for(var j = i + 1; j < n; j++) {
      if((arr[i] == arr[j]) || Math.abs(arr[i] - arr[j]) == j - i) {
        return false;
      }
    }
  }
  return true;
}
function queen1() {
  var arr = [];

  for(arr[0] = 1; arr[0] <= 4; arr[0]++) {
    for(arr[1] = 1; arr[1] <= 4; arr[1]++) {
      for(arr[2] = 1; arr[2] <= 4; arr[2]++) {
        for(arr[3] = 1; arr[3] <= 4; arr[3]++) {
          if(!check1(arr, 4)) {
            continue;
          } else {
            console.log(arr);
          }
        }
      }
    }
  }
}

queen1();
//[ 2, 4, 1, 3 ]
//[ 3, 1, 4, 2 ]

function check2(arr, n) {
  for(var i = 0; i <= n - 1; i++) {
    if((Math.abs(arr[i] - arr[n]) == n - i) || (arr[i] == arr[n])) {
      return false;
    }
  }
  return true;
}

function queen2() {
  var arr = [];

  for(arr[0] = 1; arr[0] <= 4; arr[0]++) {
    for(arr[1] = 1; arr[1] <= 4; arr[1]++) {
      if(!check2(arr, 1)) continue; //擺兩個(gè)皇后產(chǎn)生沖突的情況
      for(arr[2] = 1; arr[2] <= 4; arr[2]++) {
        if(!check2(arr, 2)) continue; //擺三個(gè)皇后產(chǎn)生沖突的情況
        for(arr[3] = 1; arr[3] <= 4; arr[3]++) {
          if(!check2(arr, 3)) {
            continue;
          } else {
            console.log(arr);
          }
        }
      }
    }
  }
}

queen2();
//[ 2, 4, 1, 3 ]
//[ 3, 1, 4, 2 ]

while(k > 0 『有路可走』 and 『未達(dá)到目標(biāo)』) { // k > 0 有路可走
  if(k > n) { // 搜索到葉子節(jié)點(diǎn)
    // 搜索到一個(gè)解，輸出
  } else {
    //a[k]第一個(gè)可能的值
    while(『a[k]在不滿足約束條件且在搜索空間內(nèi)』) {
      // a[k]下一個(gè)可能的值
    }
    if(『a[k]在搜索空間內(nèi)』) {
      // 標(biāo)示占用的資源
      // k = k + 1;
    } else {
      // 清理所占的狀態(tài)空間
      // k = k - 1;
    }
  }
}

function backdate(n) {
  var arr = [];

  var k = 1; // 第n的皇后
  arr[0] = 1;

  while(k > 0) {

    arr[k-1] = arr[k-1] + 1;
    while((arr[k-1] <= n) && (!check2(arr, k-1))) {
      arr[k-1] = arr[k-1] + 1;
    }
    // 這個(gè)皇后滿足了約束條件，進(jìn)行下一步判斷

    if(arr[k-1] <= n) {
      if(k == n) { // 第n個(gè)皇后
        console.log(arr);
      } else {
        k = k + 1; // 下一個(gè)皇后
        arr[k-1] = 0;
      }
    } else {
      k = k - 1; // 回溯，上一個(gè)皇后
    }
  }
}

backdate(4);
//[ 2, 4, 1, 3 ]
//[ 3, 1, 4, 2 ]

var arr = [], n = 4;
function backtrack(k) {
  if(k > n) {
    console.log(arr);
  } else {
    for(var i = 1;i <= n; i++) {
      arr[k-1] = i;
      if(check2(arr, k-1)) {
        backtrack(k + 1);
      }
    }
  }
}

backtrack(1);
//[ 2, 4, 1, 3 ]
//[ 3, 1, 4, 2 ]

ambRun(function(amb, fail) {

  // 約束條件方法
  function linked(s1, s2) {
    return s1.slice(-1) == s2.slice(0, 1);
  }

  // 注入數(shù)據(jù)列表
  var w1 = amb(["the", "that", "a"]);
  var w2 = amb(["frog", "elephant", "thing"]);
  var w3 = amb(["walked", "treaded", "grows"]);
  var w4 = amb(["slowly", "quickly"]);

  // 執(zhí)行程序
  if (!(linked(w1, w2) && linked(w2, w3) && linked(w3, w4))) fail();

  console.log([w1, w2, w3, w4].join(' '));
  // "that thing grows slowly"
});

function ambRun(func) {
  var choices = [];
  var index;

  function amb(values) {
    if (values.length == 0) {
      fail();
    }
    if (index == choices.length) {
      choices.push({i: 0,
        count: values.length});
    }
    var choice = choices[index++];
    return values[choice.i];
  }

  function fail() { throw fail; }

  while (true) {
    try {
      index = 0;
      return func(amb, fail);
    } catch (e) {
      if (e != fail) {
        throw e;
      }
      var choice;

      while ((choice = choices.pop()) && ++choice.i == choice.count) {}
      if (choice == undefined) {
        return undefined;
      }
      choices.push(choice);
    }
  }
}

ambRun(function(amb, fail){
  var N = 4;
  var arr = [];
  var turn = [];
  for(var n = 0; n < N; n++) {
    turn[turn.length] = n + 1;
  }
  while(n--) {
    arr[arr.length] = amb(turn);
  }
  for (var i = 0; i < N; ++i) {
    for (var j = i + 1; j < N; ++j) {
      var a = arr[i], b = arr[j];
      if (a == b || Math.abs(a - b) == j - i) fail();
    }
  }
  console.log(arr);
  fail();
});

'use strict';
var queens = function (boarderSize) {
 // 用遞歸生成一個(gè)start到end的Array
 var interval = function (start, end) {
  if (start > end) { return []; }
  return interval(start, end - 1).concat(end);
 };
 // 檢查一個(gè)組合是否有效
 var isValid = function (queenCol) {
  // 檢查兩個(gè)位置是否有沖突
  var isSafe = function (pointA, pointB) {
   var slope = (pointA.row - pointB.row) / (pointA.col - pointB.col);
   if ((0 === slope) || (1 === slope) || (-1 === slope)) { return false; }
   return true;
  };
  var len = queenCol.length;
  var pointToCompare = {
   row: queenCol[len - 1],
   col: len
  };
  // 先slice出除了最后一列的數(shù)組，然后依次測(cè)試每列的點(diǎn)和待測(cè)點(diǎn)是否有沖突，最后合并測(cè)試結(jié)果
  return queenCol
   .slice(0, len - 1)
   .map(function (row, index) {
    return isSafe({row: row, col: index + 1}, pointToCompare);
   })
   .reduce(function (a, b) {
    return a && b;
   });
 };
 // 遞歸地去一列一列生成符合規(guī)則的組合
 var queenCols = function (size) {
  if (1 === size) {
   return interval(1, boarderSize).map(function (i) { return [i]; });
  }
  // 先把之前所有符合規(guī)則的列組成的集合再擴(kuò)展一列，然后用reduce降維，最后用isValid過(guò)濾掉不符合規(guī)則的組合
  return queenCols(size - 1)
   .map(function (queenCol) {
    return interval(1, boarderSize).map(function (row) {
     return queenCol.concat(row);
    });
   })
   .reduce(function (a, b) {
    return a.concat(b);
   })
   .filter(isValid);
 };
 // queens函數(shù)入口
 return queenCols(boarderSize);
};

console.log(queens(8));
// 輸出結(jié)果:
// [ [ 1, 5, 8, 6, 3, 7, 2, 4 ],
//  [ 1, 6, 8, 3, 7, 4, 2, 5 ],
//  ...
//  [ 8, 3, 1, 6, 2, 5, 7, 4 ],
//  [ 8, 4, 1, 3, 6, 2, 7, 5 ] ]