Bridges

bridges.js

var north = [2, 5, 3, 3, 3, 1, 8, 2, 6, 7, 6];
var south = [1, 2, 5, 3, 4, 1, 7, 8, 2, 5, 6];

var nLen = north.length;
var sLen = south.length;
var matrix = [];

for (var i = 0; i <= nLen; i++) {
   matrix[i] = [];
   for (var j = 0; j <= sLen; j++) {
       matrix[i][j] = 0;
   }
}


for (var i = 0; i < nLen; i++) {
   for (var j = 0; j < sLen; j++) {
       if (north[i] == south[j]) {
           matrix[i + 1][j + 1] = Math.max(matrix[i + 1][j], matrix[i][j + 1]) + 1;
       }
       else {
           matrix[i + 1][j + 1] = Math.max(matrix[i][j + 1], matrix[i + 1][j]);
       }
   }
}

console.log(matrix[nLen][sLen]);